I've got the Tritium GS and it's superb, I can't say enough good things about it. Quality is outstanding, it does everything well and Grex's customer service is excellent.
The standard needle is .3 mm which covers most peoples needs. I use the .2 mm because of the amount of mottling I do on LW birds but if you do use this needle you'll have to use a paint that you can thin down a lot, I use Mr. Color which goes down great thin but other paints sometimes give me trouble.