It's different for everyone of course, but I've always found Mario games boring. They just lacked any interesting design or levels for me. Sonic though, has always had different mechanics to deal with in every game as each act focused on different things. Whereas Mario used the same slightly different textured blocks in each world and featured tye same mechanics (jump over hammers, get coin, avoid enemy etc). It's why I preferred Rare's platformers on the N64 too.
I've only enjoyed Mario Games starting as early as the NES with SMB. of course and stopping as late as Mario 64(in my opinion, the last true SOLID Mario title just like N64 was Nintendo's LAST good console). But 1989/1990's Super Mario Bros. 3 is still a wonder of gaming perfection. It is one of the most noteworthy platformers in history if not, the greatest game of all time.
Regarding Sonic, yeah I was there at the beginning back in '91. Sonic 1 in my book WON hands down over Super Mario World which is overrated,linear and too shallow of a platformer to really enjoy or want to replay. Believe me, in 1991 I got a Super Nintendo for Christmas brand new, and I actually broke my NES to try to convince my stepdad that SNES and NES weren't the same thing and keep in mind $200 in 1991 is $400 today.
Only 1 day into playing SMW, buyer's remorse set in. The biggest issue I had was the 2 HIT Mario 1 life cycle. It drove me insane for 11 years. Why the hell did Nintendo of America give Mario 3 a 3 Hit system in 1989, but revert back to the Mario 1. 2 HIT system with the next game after that??
On top of that, the level design was arbitrary and linear. When I played Sonic 1 on the $150 Genesis purchased by the Husband of my Mom's friend earlier that summer, I found it fast,furious,FUN and unique.
Regarding SEGA trying new formulas for Sonic games making them different each time. There's nothing wrong with that. This is the type of attitude of why Call of Duty is so successful. Recycling the same formulas over and over again. Selling your morals for money and pleasing gamers by putting out the same JUNK year after year. I haven't played a Mario game since 64, and there's a reason why. Trying new things and being different is okay. It's disgusting to think that people think that SEGA should just be like everyone else. That MONEY to them is more important then creating unique gameplay and being innovative.
SEGA keeps trying new things, and I am proud they aren't listening to the Sonic fanatics. As far as I'm concerned, if they keep complaining and whining that Sonic should be the same every year, rinse,lather,repeat with nothing new, nothing UNIQUE and NOTHING innovative, then Sega should drop them like a bad habit.
Sonic is NOT Mario, and he SHOULDN'T be like Call of Duty or Madden. If SEGA were to have done exactly what these so called "fans" want, the novelty and appeal of Sonic in general would have run out of steam years ago.