If you can only get 2, get Hulk and either Cap or BW. If you’re planning to T3 Cap, then definitely get his uni. The other unis are pretty “meh” and not really worth it.
Magneto doesn’t really have that one hard hitting skill that would synergise with a damage proc, so he would benefit more from something like a CTP of Transcendence, which gives him a solid damage boost with an all attack increase and the invincibility makes him a pain in the ass in AC.
For Jean, if you’re building her for PVE, go double fire damage + proc. If you’re building her for PVP, try to roll a GBI + fire damage + invincibility. For a balanced PVP and PVE build, try to roll a GBI + fire damage + proc obelisk. A CTP of Destruction would also be good for her in a balanced build. I’ve also heard that she does well in PVP with a CTP of Transcendence.