For official nintendo games, my favourite is Super Mario World and SMB3.
For unofficial games, I have played many Rom hacks of SMW, and SMBX as well.
By the way, one thing I don't like SMBX is its physics. I prefer the physics in SMW much more than that in SMBX, because SMW's physics is way more agile (I mean Mario is having better acceleration there). For reference, you can see Mario's agility in the final boss of Kaizo Mario 3 (
https://www.youtube.com/watch?v=oYHlznTM2zo). As a comparison, the final boss of SMBX's Princess Cliche 2 is much higher to fight (without hammer suit and bullet bill gun) simply because Mario doesn't have enough acceleration (even if Mario has enough max speed) to dodge the flying koopas (and has a bigger hit box).
I wonder if it's possible to include an additional configuration pack which implements SMW game-play physics instead of replicating all standards of SMBX.
The ghost houses, the secret exits, the switch palaces, the cape... And it actually felt like a big adventure as well, unlike others I've played... Yeah. It's memorable, it's fun to play, and always brings a smile to my face every time.
And SMW's gimmicks, but not as much as the graphics. They are less detailed than the ones in SMB1. If we combine SMB1's graphics with SMW's adventure it will be definitely my favourite 2d mario game! 
1)/elempow=linux/atktype=rang+mel/5df/5at/5sp/arm=none/wep=orders/maxhp=100
)/elempow=sound/atktype=ranged/5df/8at/7sp/arm=none/wep=mic/maxhp=100
(this was made by rsuper)
