Leveling in this game has always been an "interesting" part of the game.
I for one have always hated leveling up, because the part between 47 and 55 is just a pure terror for me, and the majority of the players.
I started playing on the pre-open beta server about a year ago now, and I've made a few lv70 characters with the support of my friends, and we've managed to find some very good spots to boost your EXP.
I personally like to count exactly how much EXP I get per mob, and compare it to the quest's exp reward that I would get, and if I can get the double amount of exp from normal grinding, then I will just grind (+ do the quests for the mobs im hunting for.).
Now, powerleveling is a different way of leveling, and it has some requirements that you must have, if you want to do it effectively.
1.) You need to have a level 70 character that is able to do huge damage, and taske some damage aswell from the mobs.
2.) You need to have patience, powerleveling is faster than questing, but it is nowhere near perfect.
3.) Experience boosters are a key to do it faster obviously.
I have a level 70 turtle hermit, a level 70 karma majin, so I use those as examples, I don't know about plasma or DW whatsoever.
Level 1-22 is always the same for everyone, just stay around your spawn point, look for 2-3 higher level mobs than what you are, and keep killing them in 1v1 until you get like level 4 or 5.
Basically the first 22 is level where you just get the high amount of exp for using 2 skill on a mob, on these levels you are better with quests than mobs.
If you don't feel like spamming potions and skills, do the quests, you can get to 22 in about 2 hours.
If you feel like killing, then bring your high level character, and go to the local dungeon, [on the starter maps, there are dungeons that you are required to go, to get your 7th quest dragon ball.] and you can just grind there, that's a very effective way aswell.
UD1 normal up to level 28, make sure to alwaays stay a bit behind, because some of the bulls are using aoe damage, and you can get 1 shotted.
28 to 31, on RP1 this spot.
Just kill everything you can, then move to a safe spot, change channel, do the same. The mobs respawn time is a bit long, maybe about 4-5 minutes, so you can take your time on each channel. You will need to stay here until level 31, [And make sure to use your 100% exp boost a little bit before turning into 31, this is very important!!]
Once you hit 31, you will head to our good friend UD1, and you will need to go to Hard this time, which is cool because not only you get lots of exp, but you also can get legendary gloves / staff for youself, which is very useful as you level up, since there are always levels where you gotta quest.
You will stay here until 33 or 34, depending on how much you hate your life after returning to UD1, because trust me, after this journey you won't ever go near UD1.
ALTERNATIVELY, You can do ud1 normal up to 25, then spam TMQ1 hard, for the insane exp, and chance of getting lots of stones + legendary armor, which you can either sell, or use.
34 to 38 is full of questing, you can finish RP1, you can do westland, anything you like, you're loaded with awesome exp reward quests to do.
38 to 44 is RP2, where not only you can powerlevel yourself, you also can get good gear for your level, also lots of exp, and lots of KD and stun, what a joy. RP2 quests alone give you a full level, so if we count the amount of EXP you can get whilst questing, or farming the frogs, you should be fine up to 44.
44 to 45 is questing aswell, but you can also do tmq3 hard if you feel like, however, i personally think questing would be faster.
45 to 52 is everyone's favorite thing to do, "party para ud3?" UD3 easy, ye, if you haven't seen enough bugs with the skills, you will definitely see LOTS of bugs now, that for some reason bleed you. Spamming the first floor of ud3 is a very effective way of advancing, and also very easy.
Here is the trash part of the leveling. Most people run out of quests, or the quests they get is terrible, and it is a pain in the background to advance, I personally quit because I had to do it without having master class, or even crit%, so lel.
52 is the time you go TMQ4, however,you don't want to finish it. TMQ4 has a system where after beating Nappa, the next quest you get is to kill the turrets, which is you don't do, the soldiers around the turret will keep respawning.
You have 9 minutes to kill two of them, so what you want to do is, pull the soldiers around the turrets, and make sure that your skill will NOT damage the turret, because you might end up finishing the quest, and you failed the plan.
Pull the mobs, as many as you can, and make sure that you CAN tank their damage, they don't poison, no stun, no confuse, no debuff, only thing that can be annoying is the fact that they each have 40.000 to 60.000 LP, nothing else.
Each mob you kill will give you EXP [without 30% exp boost] so basically 3 group of mobs is 13293 EXP [17280 with exp boost], and it takes you about 30 seconds to kill them.
Now, im UD3 easy, even with exp boost, you take atleast 1-2 minute in the dungeon, + the teleporting time, healing the shit etc, you get only 21074 exp, so it's quite easy to count which way works better.
Keep pulling the mobs and you will get about 1 bar a run, [also make sure that they powerleveled person always has the quest for TMQ4 normal, so you can get the quest whilst boosting him/her].
You stay here until 54, then UD2 hard up to 57.
This is the part that heavily depends on you, as I personally prefer to do dark namek quests until 60, and then grind up to 65 on papaya island, like anywhere, on papaya you can always find spots to grind.
However, I for one prefer this spot, as there are LOTS of mobs, that give 720 exp, and they are level 65, so you can keep grinding here up to 66 if you want.
66 to 70 is questing, ofc.
I mean, UD2 is muuuch easier for 38-45 since every run is like half a level with the EXP boost.
For 52-54 I found this awesome place that you can abuse (no ALTS needed) in the Red Map! I think the place is called "Yoseri Lake"or something (Sorry, not on PC to get the picture but I will edit it when I have the Pic)
That place is MOB-RICH, everything gives amazing amounts of EXP, since killing 1group would result in around 7500 EXP per group (Takes less than a minute per group)
If you have a Character that can hunt hard (say: Turtle, Crane, DW, SK (not really since you wont have 100% potential in skills), Karma (pure Form Genocide), Plasma, Grand Chef also has AoEs which I tried, but they need more rest than other classes!)
The place is a gold mine if you have a decent class, but otherwise, as you said, TMQ is better.
UD3 Hard can be taken to lvl 60, but to be honest, it gets WAAAAAAAAAY too boring. I rather do Dark Namek Quests or Hunt my way in Papaya (the Crocodile Place) around lvl 58 to get stuff done easy.
Let's say you're a lv70 turtle hermit, fighter, swordsman, anything. And your alt is a lv38~45 character [we're talking about ud2 easy now]. You use your lv70 to damage the boss down to about 10000 LP, then stun him, then dash back to the far end to lose target, so your lv38-45 can kill the boss, and he'll get the 100% exp, which is 30k exp in easy mode, 60k in hard. This is a veeeery effective way of geveling up quick.
38-45 can be all done in UD2. You can get around 1 level up per 20 or even less minutes.
RP2 as a place is a genuine bad experience. The place in my opinion is only useful if you have someone who can blast everything away with 1 hit, even then, if that's the case (if they are powerful enough) then they can solo UD2 and take you there for much quicker leveling.
Sorry for possible grammar errors, English is my 3rd language.
Please also do note that I am nowhere "professional" on leveling, or anything, I just shared my ways of leveling.
Sorry if I missed some important information.
oh and fak tmq4