If you have already got Emma, her uni is awesome. If not, skip it and get the other uni
Emma is second best for Maw after Wanda and damage-wise next to Psylocke but with better suvivability.
And yeah, she is luxury but if you can do SL stage 30 its a luxury that is worth it imho <3
For UWB , QS is 1st just insane damage top tier. Then X force X-23 For proxima and corvus uwb. Both IM and WM have dps for UWB but you might have difficulty keeping alive on higher stages. BD or cull Obsidian and AV is good for say first 15 stages of proxima but latter lack dps or can be one killed. Proxima , collossus and archangel are not very good for uwb. Magneto is good for lower stages of cull.
Both Emma and Warlock are an unnesseccary luxury.
Emma and Warlock aren’t worth it imo, especially if you’re F2P. Neither of them are game changing even with uni and there are other characters that can fulfill their roles who can be built for much less of a cost.
Magnetos uni is a definite improvement on the base kit, but it’s not a huge improvement. It’s not a must have by any means. It is, however, one of the best looking unis in the game imo.
Generally, I would rate the above unis in this order :-
IW Spidey > QS > IW Iron Man > IW War Machine > Proxima > X23 > Archangel > Black Dwarf > Agent Venom > Colossus > Magneto.
However, since you asked in terms of WBU, I’d rate them :-
QS > Iron Man > War Machine > X23 > Archangel > Spidey > Black Dwarf > Agent Venom > Colossus > Magneto > Proxima.