Getting rebel models

I have CS:S, TF2, Portal, and Gmod. I want to modify the rebel skins, but it won’t let me, and as far as I’ve heard, I need one of the HL2 games for the models.
Which one should I get: HL2, Episode 1, or Episode 2?

P.S put them in order of first to last.

it doesn’t matter which, the models are the same.

The rebels should be with GMod. But above is right, theyr’e the same for all games. I’d advise getting them in the order you posted to understand the story. You should also get HL1 first.

Get the Orange Box, save money.

^Better idea

You already have those models if you have one source game. All source games mount the HL2 content (excluding maps). The models will be found in source models.gcf.