Copyright isn't an issue, you can't copyright a game mechanic, that's settled law.
As to your question, IMO Tribes 2 is the 'best' Tribes Ascend is probably the most accessible to new people.
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Tribes 2 for multiplayer and vehicle + equipment packs. Tribes Vengeance for Campaign and skiing physics + grapple hook Source link
I had most fun with T:A, enjoyed T1 back then. T2 never really made me warm for it's kind of clumsy movement […]
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