I own a Daytona Twin, and I've haven't played Rush much,
so my opinion is probably biased, but from what I know (...and have been told),
Daytona is better for actual "racing feel" and the driving dynamics (drifting, feedback, etc..)
are more realistic. (ie. more like real racing than a driving "game" ).
[ I also have a Cruis'n USA, and that really is a "game", nothing realistic there...]
That said, Daytona has limited track selection ( 1 oval, 1 easy track, 1 hard track),
and only one car.
Rush has alot more options (both cars and tracks).
Like others have posted, for an actual "racing feel", go for the Daytona,
but for variety and longevity, you might be better off with a Rush.
That said, I probably would not trade my Daytona for a Rush if offered...
Tough choice...
Good luck.
Steph