my gut reaction was Coleman without a doubt, but Arlovski has been fighting such high level guys that's its closer to even than you might think.
Coleman got his doors blown off by Mirko, Fedor, Shogun, Randy and nog. so basically mark lost to every great fighter he faced in their primes.
Andrei lost to Sylvia, Sergei, Fedor, Bigfoot and Rizzo.
coleman lost to better names I guess but they both lost to every great fighter they faced. Andrei won some nice fights in devastating fashion which makes it easier to remember his victories over somebody like Coleman who isn't flashy at all.
I guess its definitely Coleman all the way, but Andrei has had a decent career.