I guess it depends on what you mean by "tighter." I think it's indisputable that when Sonic is bad, it's really bad.
I submit that when Sonic is good, however, it hits far higher highs than the best Mario course. Sonic at its best is sublime. I've heard people compare it to F-Zero in the sense that the player must have a complete mastery of both the speed of Sonic/the racer and of the course to make high-level runs. I tend to agree with that (and I also really love F-Zero because of the speed and the exacting nature of the courses). A great Sonic course is very tight and quite exacting in a way that Mario can't reach simply because the nature of Mario platformers are different than Sonic platformers.
Mario at its best has some really fun courses, but I wouldn't say that they give me any more satisfaction to complete than strong courses in a good indie platformer - something like Super Meat Boy has better timing-based obstacle courses in it than any Mario game since SMB3.
What I really like about Mario is exploration, actually, since Nintendo actually seems to understand how to make it rewarding without being repetitive. They make better collectathons than Rare ever did, which makes it a shame that after Sunshine, they've gone away from that quite a bit (though SMG2 did a fair, if not great, job with exploration via some of the better Green Stars).