Koei Mosou/Warriors games have only one problem, they're a bit clunky compared to their Capcom counterpart.
SB is more frenzy action-packed, has one of the most stylish (it's capcom after all!) and crazy character rooster (teens, emos, gender benders, mechs...) ever and is a bit more "bright and colorful"!
SW is fun to play because stages actually require a bit more strategy to be completed, and the overall design is stylish too, but more "classic".
Don't get me wrong, I love it too, I finished every Dynasty Warriors from 4 to 6 and every Samurai Warriors (including Empires and other expansions) and I'm looking forward to SW3 to be ported to PS3, since now we have Move!
But Sengoku Basara is just more fun to play to me!