I played both, not sure which is best from memory, but i distinctly recall the first time i played SMW. I had not played any platformer games in years and years, and sat down to SWM at my sister's house one afternoon, all alone in the house, haha, with an absolute blazing head splitting hangover from the depths of hell...but i played through about 25-30 levels of the game that afternoon, with no booze or drugs to take the edge off the hangover i had to settle for SMW, haha. But, aye, i enjoyed all of the Mario platformers.
Also, you had that great Mario rip off game 'The Great Giana Sisters' that was banned, I had an illegal copy of that for the Commodore Amiga, it was as good as the actual original Mario platformer it ripped off, loved that game. I mean, it had it's own level designs and all that, it was just the actual style of game was wholesale ripped off.