We have had Cosco Alpha Omega car seat since she moved out of the carrier. She is 7 1/2 and still in that as a booster. The five-point harness system was great and we used that until this school year. This summer I took the base and five-point harness off and now we use it as just a booster, but it still has the high back and side wings, which are great for napping.
We bought one for each car and grandma's too. All are still in use the same way.
Someone gave us a Greco Turbo booster seat, but it's impossible for her to nap (sits in the middle seat to keep her way from side impact airbags) that she HATES it. She'll ride in that for short trips (running to a class or the store), but on a trip more than 10 minutes, she climbs in her Alpha Omega.
Stephanie