Well, I never played the first game...
...excluding one time when I rented it, but that was when I wuz to young 2 really understand it, or get the controls down, you mean? Then, later on in life, i bought B/t, and was blown away by it!!
I would choose Spiral Mountain for the first (?? lol).
A (first game):
In spiral mountain, you'd start at banjo's house, and the level would scroll vertically (that's sideways, right? lol, brainfart) to the first bridge, crossing the stream. Then, you'd be running/ fighting you're way up spiral mountain (slowly, no need 2 rush), and when it got to the bridge, you'd be forced to cross, with Grunty on her broomstick sweeping down now and then like in the boss fight with her (I saw the fight, not played it, wish I had), and once across the bridge, you'd enter Gruntilda Winkybunion's castle lobby. Cheato would be flapping around, serving as a platform kinda like pidget's in kingdom 2 in ssbm... Then, the level would end at mumbo's mountain. The screen would stay still for a while, then maybe backtrack down the mountain, back 2 banjo's house, and then re-backtrack (??)...lol...
B (1st level):
The top of grunty's castle, where the boss fight is, and with the boss music going (I LOVE THAT MUSIC) Grunty would attack like in the real game, blasting you with green magical spells, and maybe every once in a while, the jinjonator will appear, and dive about randomly in the air...
BANjo-Tooie...
I'd have to go with hailfire peaks. I absolutely LOVED that level. It would be a nonscrolling level, situatied primarily at the entrance to the world is (lava side). The fire dragon would be spitting at you every 10 seconds or so, just like in the real game... Then, after a while of fighting, the players would be sucked into the warp pad (or something like that), and would be teleported to the icy side, where they would fight...um...somewhere...I can't really remember the icy side, except for icicle grotto and the generator thing 4 Grunty Industries...so, IDK where you'd fight there...but on the icy side, the ice dragon would spit ice shards at you every 10 seconds or so, just like the original game...lol
I know you didn't ask for my life story but...
Tell me what you think!!