We got a Hipod one (MaxiRiders etc are just waaay too bog for our car and too exxy)
She loves it, you can use a harness or the regular seatbelt once they are tall enough, has the cup holders (again a novelty she loves lol) and speakers in it, so I can plug my ipod into it for her and WE can get a break form the nursery rhymes while she sings along to them happily!! lol (joy!)
It is height adjustable and will last her til she is 7 easily.