I just downloaded the Split Second PC demo and it isn't half bad. Very much a 'What if Michael Bay made a Need for Speed game' concept as there are so many explosions going on. Ended up crashing my car at one point because I couldn't see the turn through all the fiery pyrotechnics. Unfortunately, it's only got 2 play split screen.
Blur looks pretty insane too though the offensive gameplay leans more to traditional kart racing and with 20 player online games and 4 player split screen.
Not sure which one's better but one thing is for sure, we're not going to short on action racing games for a while.