I think it totally depends. I have tried at least 5 different car seats since I got Tate. He now rides without one. If you have a small dog it's allot easier. Tate is about 20lbs (I know he's huge for a Yorkie) and cannot sit still enough in alot of seats and ends up tangling himself up in the teather. For dogs who are better behaved in a car I would totally reccomend the Solvit car seat(see my photo album of Tate in it as a puppy). It is probably the most stable. We tried the traveling dog which didn't work because tate is too heavy so it kept collapsing
We also tried another one from Petsmart that you have to blow up the bottom in order for it to boost your dog up high enough to see out the window. I can't really explain it here but this thing is a disaster!
I now occasionally just use a special tether that hooks to the seatbelt. Just remember to always use a harness with these things. Never attach from the collar!