So xforce is the only 4* character I have max covers for. I have max covers for the majority of 3* characters. So which direction is more beneficial? Thanks
It depends on which 3s, and on what level your XF is currently, but I’d lean towards 3s.
Cyke, Groot, Khan, Scarlet Witch, Iron Fist, all worthy of ISO right now. Plus the old staples, Patch, Thor, BP, L.Cap.
If you had that entire list maxed out already, then maybe XF.
I’d vote 3*s also, both because I like them more ( 
) but also because the game is quite punishing on outlying characters - you will see higher levels across all modes for having a L260 top of your roster (and a few bits of broken scaling I believe e.g. The Gauntlet?), but of course you won’t actually want to use X-Force in all your matches.
It probably costs very little now to get X-Force to L166 now, so do that as a taster - see if he wows you or if you find him no more interesting than your other characters. 
Lerysh I have a majority of all the 3* max covers and sitting between level 100 135 between various characters.
Thevulture my xforce is currently at 166 and to max him is 306k ISO and I’m sitting on 320k. U make a great point about being punished for lvl 260 character. Thanks for all your replies