MajinRow it is really up to will game be changed.
That is, will aggro system/class balance /party system or party meta change.
Soo lets asume that it won't be changed and game after wipe will be good for month or two.
You will need then to ditch DW and SK and take Karma Majin or Ultimate Majin for PVP and PVE aspect of the game.
Both of them are needed for party PVP and PVE and they are good when you want to farm.
Soo as someone new to the game and as someone who will have hard time to gear up, I suggest you to play as Karma Majin.
Since you won't need to raise armor too high and you only need speed weapons to be part of party with no problem, you will have easy time to gear up. Another thing is, that you can easy switch from PVE build to PVP build and since karma is one of the most broken classes in game with ultimate in top tier, you will enjoy the PVP too.
Why you shouldn't play DW or SK?
Mostly in party, because almost any class well geared can replace the tanker, tankers become the shit in PVE soo you will have hard time to even find party to go there.
About PVP, you will be decent with them but you will need to spend tons of time, zeni to get all the gears to even be able to face all other race/classes and still you will face the broken ones or ones that not only counter you, it simply trash you soo without luck or right gear and build and good strategy you will mostly lose to them.
All in all, you need to take all around race/class that is needed in party for PVP Budokai (mudosa points aka mudosa gambler and accessory and cool stuffs), PVE ( Dungeons, TMQ, CCBD soo you can get tons of boxes, legendary gears or accessory and dogi balls).
Soo for this case, the namek tankers, do not fit this role due bad party system, multi client and aggro system and PVE in general that does not favor or need true tankers to be part of it.