I have a tripp trapp and a plastic Ikea one with tray for my daughters and they are both brilliant.
http://www.ikea.com/gb/en/catalog/products/00069725
The tripp trapp because the height adjusts, my eldest daughter sits up straight and well in it and it is quite discreet having it tucked under the table. Also nice having her sit right up at the table when we are eating together. She is now 4 and still sits on it but without the bar and back support. It's a great height for her and very comfortable which is great becuase she likes to sit at the table for ages drawing or doing play doh etc
Although not the cheapest, been great value for money and the wood still looks new 4 years on.
The Ikea one because it is light and movable, the legs and tray clip off and very easy to take out to friends' houses. We had it as an extra and although I always intended to buy a second trip trap for my second daughter, we have ended up using this and she sits very well in it and the tray doesn't protrude out too far like some of the semi circle shape ones. You can also buy a foam type insert for back support.
If I had to choose - think it would be the Tripp Trapp because of the longevity but the Ikea one is a very close second!