Can’t really make a comparison. NES mostly has still very arcadey, simple games, while SNES is the generation where games started becoming longer, more complex and engrossing, but also less immediate, less “pure”.
Like, I love Megaman X1 to bits, but no MM game that came after the NES recaptured the same feeling and gameplay of the original series - with the exception of the phenomenal MM9, and I don’t have to tell you that MM9 is basically a NES game.
Many problems in NES games came from lack of refinement and QoL features, plus the retarded changes to balance and difficulty a lot of games underwent in the transition from Japan to US because of rentals. Games like Metroid and Kid Icarus are significantly better in their original Disk System version thanks to saves - passwords were a chore to write down, and to this day I swear some passwords I did copy correctly didn’t work. Imagine how my heart sank when a password from the second-to-last level in Kid Icarus didn’t work. But apart from these problems, those games are still fun to play. Metroid was a little less brutal in its Japanese version too, I’d love for Nintendo to make those FDS versions available outside Japan at last.
When SNES came along, the widespread adoption of battery saves meant games had to become longer to not be completed over a weekend, but it also meant they got more bloated. And many games were still rooted in 8-bit gameplay anyway. The Super Famicom Dragon Quest games still had all the grinding and the limited saves of their NES precursors, and were mostly much longer and more bloated. FF4 is a NES game on steroids. Basically, all the game genres that were typical of home gaming got undeniably better in the 16-bit era, but also lost something in their evolution. People fawn over Castlevania IV, but I find that game slow and boring compared to CV3 (or even the original, which I never completed without savestates but it’s great to kill half an hour).
On the other hand, purely arcade games really bloomed on SNES. NES ports from arcades simply couldn’t compete with the originals unless the game was specifically repurposed for the home version, like Contra. But space shooters on the SNES are leagues better than almost every single one of their NES counterparts, from Parodius to R-Type to... practically anything you can name. There‘s very few shooters I can play for more than 5 minutes on the NES, but on the 16-bits (and the PC-Engine) I can spend days blasting space monsters into oblivion. And fighting games, well... the NES had Double Dragon, OK, but the SNES had everything, and when one-on-one fighters exploded with SF2, the older hardware had nothing to come back to.
To answer OP’s question, I’ll have to go with SNES because when push comes to shove, there’s little I can replay to completion on the NES in its original state without savestates and such. Everything Megaman and Mario, sure, and Kid Icarus, and a few others. But it’s rare that I go that far into Metroid before ragequitting, and top-down NES RPGs are a chore (but please have a look into sideview action RPGs like Faxanadu or The Battle of Olympus, those are still great games). OTOH, I’ll rarely say no to a quick dive into SNES games when I don’t feel like playing for more than an hour.
