I'll happen to actually own a surprising amount of 3rd party multi-system games, (considering i own a total of nearly 40 cube games now, this is basicly expected)
THPS3, THPS4, SSX tricky, SSX 3, Burnout 2, Timesplitters 2, Prince of Persia, Metal Arms (amazing game if you haven't played it yet) Soul Caliber 2 and Star Wars: bounty hunter (which, honestly, isn't a good game) and as of last week, Beyond Good and Evil (great game, great game)
Now, each of those games has sold decently well on gamecube compared to the other systems, (likewise, I really don't think burnout, PoP, or metal arms sold well on any system.)
None of those games (with the exception of bounty hunter) are anywhere near bad titles, they are all far above average in my book.
however, that does mean that the other 30ish games i own ARE cube exclusive, (and about 1/3 of those are first party) which means that its pretty obvious that cube geared games are what i prefer. However, just becuase something is multisystem, doesn't instantly make it bad. If i was making a game, i'd most likely try to have it accessible on all systems, bigger market means a bigger profit hopefully. Likewise, this is also why bad games tend to be marketed with cheap ports.
Overall, i had a very annoyingly large post over on the ocremix boards about why certain games don't sell well, among other thing nintendo related, mainly about how many 3rd parties are no longer producing for the gamecube because theyre games didn't sell.
overall, the entire thing boiled down to "Gamecube Owners aren't ****ty games target audience" and i hold true to that.
anyway, i don't want to drag this on much, but i would suggest grabbing the cube version of any given title myself, simply cause i like the controller better, unless another version has some mad extra's.