We got a really basic one at first but DD hated it - seemed very low for her. DH got obsessed by the fact that it couldn't be comfortable and (despite lots of eye rolling from me) went out & bought the Baby Bjorn one for his little darling... who took to it straight away --little traitor--
DS refused to use the cheap basic one so I ended up getting the BabyBjorn (two in fact as he liked it so much). He likes it so much he still uses it although he's nearly 4. DD (2) actually likes the basic one that DS wouldn't use so she's now using it. Really depends on the child. I like the BabyBjorn one as it has an insert you can remove to dump its contents so quite handy, and sits very solidly on the floor so less risk of spillage when DCs stand up.