My friend has always used one of those travel booster seats. However it has recently broken and she's wondering whether to bother buying another one as her DD stopped using it at 18 months and her DS isn't far off this.
depends on your table and chair I suppose. DS was out of highchair just after oneish - but he would never have been able to reach properly and been comfortabke without one if us constantly stopping to readjust him.
My parents got a new table and it is very posh and high up and he can comfortably sit on one of those with no booster or cushion at all!