That's entirely up to you.
As it stands now, Mods tend to have their own little area of expertise:
Lemur Free - Multiplayer additions
efxMod - Graphical Additions (Plus implementation of AirMod V0.5)
AirMod - Weaponry additions/modifications
Plys Mod - Scripting additions (Not really specific to any area other than scripting, but does include Dual-Wielding)
It's none of my business to tell you which one is better, that's entirely up to you to decide what it is you are looking for. Aside from Mods, there's also the latest V108 update or the V109 Betas to choose from. They include new features as well, including Headshots and adjustable Jump Height. V109 also introduced a variable system. You can find a quick run-down on it's variable system in a tutorial that I wrote for it inthe scripting board.
I think, though, while you're still learning to script, to not worry too much about which Mod or version you use. I would suggest that you try some simple scripting to start out. Perhaps look up my "Complete Newb's Guide to Scripting" either in the Script board or in Nickydude's FPSC Guide. It goes into great detail on how scripts functon and how to code them. It's also the beginning of a series of tutorials that I've written. If you follow along with the tutorials that I wrote, you'll eventually get up to doing some basic AI among other things.
If you're serious about using FPSC, then learning to script is almost required for getting what you want in your game. Don't get me wrong, though, there are still some things that require source modification to do. (Mods)
I wish you the best of luck in learning to script, and if you ever run into any troubles trying to write one, you can always post up in the Scripts board about it. I check in there rather often to see if anyone needs help.
The one and only,
