Ion if you are struggling for money and too impatient to save, but be aware that you will need to upgrade it fairly quickly and it will continually be a drain on your pocket until you have it set-up right or decide to upgrade to a different marker.
Rial if you can stretch your budget or save up as you do not need to upgrade anything on it if you don't want to, its easier to maintain, and a great paintgun based on the estalished Matrix platform. Advice on the trigger and back-cap is good, but not essential upgrades.
Whatever marker you buy, don't scrimp on your loader and air. If you buy cheap, you will realise you need to upgrade pretty quickly and will have lost cash in the process.