I think you like assassin-y characters. Rengar is pretty much the best single-target assassin/snowball champ in the game; he takes some getting used to, but you could have a lot of fun with him. He is the better top laner of the two; in fact, I would say he makes more sense at top lane, as a. more farm = more damage, b. excellent duelist/lane bully, c. his early jungle is pretty rough, and d. he likes to splitpush late game; that's kind of the top laner's job. (He's very item dependent; I recommend sword of the occult almost every game.)
Rek'Sai is my favorite jungler though; she's very consistent. I'd call her the quintessential jungler: small poke, high mobility, decent damage, decent crowd control, awesome vision control, great sustain, no mana gating. She falls off late game, but definitely a more consistent champion.