Lars is in Tekken 6 console version, and Tekken 6 BR arcade version. The only one which Lars doesn't appear in is the Tekken 6 arcade version.

Tekken 3

Tekken Tag Tournament

Tekken 4

Tekken 5

Tekken: Dark Resurrection

Tekken 6

Tekken 6: Bloodline Rebellion

Well, Tekken 5 DR is much cheaper than Tekken 6 at the moment. In Tekken 5 DR, you start with all of the characters so if you want all of them to start with go for Tekken 5 DR.

If you already have Tekken 5 for PS2, then you should get Tekken 6.

Tekken 6 has already been released. The next Tekken game, using Tekken style fighting, is Tekken Tag Team Tournament 2.