I usually stick to Frontline Plus and use Capstar on the animals that we take in from the shelter because it kills fleas within 30 minutes. 

I'm pretty religious about flea preventatives after living with my sister in her brand new house.  Apparently the yard had a severe infestation which then transferred to my 2 cats and her 2 cats.  Once we had the Frontline on them, the fleas started biting US!!! She had to bomb the house like 3 or 4 times and my dad sprayed down the entire yard with some kind of horrible chemical that kills fleas.  What a mess.