Brand and Malzahar are both easy to pick up and they work as both mid and supp, I suggest Brand even if only just for those times when you get filled for supp. As for the others, it's up to your preferences and taste really. You can use the PBE server to test any champion in the game if you'd like.
As for favorite positions.
Top - cuz I enjoy managing my waves but tower plates kinda sucked the fun out of that (although they do reward early dominance) i.e you get punished needlessly for doing certain things that used to be a top lane bread and butter for like 8 seasons straight up to that point, I also enjoy the top lane related macro.
Supp - cuz I mained it for like 3-4 seasons but also cuz I enjoy playing off meta picks in that role.
ADC - idk, dmg.