>>11911626
Sonic the Hedgehog 2 for the SEGA Master System. I know it gets a bad reputation due to the much more difficult Game Gear port, with the smaller resolution making things harder than they needed to be, but the console version with its TV resolution is a much more comfortable time, though still challenging enough to still be engaging when it comes to going for completion and all...

>>11888708
It's a good contender... but for me it's Sonic 2 (8-Bit).

>>11833954
I'd say most of Sonic's 8-Bit/handheld career was quite solid:

Sonic 1 (8-Bit)
Sonic 2 (8-Bit)
Sonic Chaos
Sonic Triple Trouble
Tails Adventure
Sonic Pocket Adventure
Sonic Advance
Sonic Advance 2
Sonic Advance 3
Sonic Rush

>>11813539
Sonic 2 on SEGA Master System.