I would try both Tribes and Tribes 2 out. Personally I loved T1, but Tribes 2 grew on me and now I prefer it. I think T2 offers far more roles and options for all types of players so they can get involved in the game.
Legions right now is not a bad game. Currently though, it plays like Tribes LT. Tribes LT was a variant of Tribes that focused on diminishing a lot of the tactical asset aspects of the game. So basically folks playing LT didn't really utilize the deployables, vehicles, inventories stations etc. People would play light armour and just play man on man with the core weapons. Its a fun gametype and popular in competition, but it also diminished a lot of the tactical roles in Tribes base gameplay.
For new people to Tribes I think you'd have more fun playing in a non LT server. Also Tribes 1 is obviously the older game so it will look a bit more dated then Tribes 2. I recommend trying out Tribes 2 by using TribesNext here.
http://www.tribesnext.com/Some T2 Gameplay
http://www.youtube.com/watch?v=b2rLOBJXrtgYou'll be able to play Tribes 1 soon enough through IA and it will all be nicely configured for you. If you want to try Tribes 1 now you can download here
http://www.tribesftw.netT1 gameplay Legeacy Pt3 had some amazing grabs in it
http://www.youtube.com/watch?v=anxi8Hvx8MI#t=20sBut T1 may require tweaking around with some scripts to get things right.