Personally I prefer the Catapult. It's a wonderful mech with excellent characteristics.
That said, I think the first thing you should look at is whether or not you prefer Ballistics over other weapon types. If Ballistics are your favourite, then definitely go with the Jagermech. They are ALL Ballistic mechs, whereas only the Catapult K2 does Ballistics.
Conversely, if you prefer missiles you should definitely go with the Catapult. It's a wonderful missile platform with great mobility (jump jets!).
The above should be your first criteria when making your decision. Love Ballistics, go Jager, love missiles, go Catapult.
Beyond that, here are the reasons I prefer the Catapult:
- The small side torsos make it a natural XL machine. You will survive a LOT longer with XL engines in a catapult than in a Jagermech. Sadly, in order to mount decent ballistics in a Jagermech you pretty much have to load an XL engine... which means you will die very quickly if focused. Catapults can get away with it much more easily.
- Jump Jets. JJs add a significant edge to a mech, and even a single JJ will make your mech significantly more mobile. Furthermore, poptarting is still very viable with LRMs, allowing you to clear many obstacles.
- Variety. The different catapult variants cover most roles extremely well.:
* Catapult C1: An excellent Missile/Energy hybrid. My favourite mech of them all. It allows you to load a TAG while STILL carrying some hefty energy firepower. Try LRM10s or 15s with PPCs or LLs or LPLs. Or 2 LRM 20s with 3 MPLs and a TAG. Or, conversely, load a couple of SRM6s and load up PPCs and MLs or MPLs. Lots of possibilities in that package.
* Catapult C4: An excellent missile boat. It's unique feature is it has 40 actual LRM tubes, allowing you to fire 2 LRM20s at once in a single "cloud". The energy hardpoints allow you to load a TAG, but since they're in the CT you are very limited. I use it for my pure LRM boat.
* Catapult A1: We all know the Splatcat, and it works. No energy HPs makes it a sub-standard LRM platform however, as it cannot mount TAG. But it certainly splats well.
* Catapult K2: Basically an energy sniper. It has 1 energy HP in each arm, which is mounted high up, just like the Jagermech, which makes it excellent for PPC sniping. It's 1 energy and 1 ballistic HP in each side torsos give it added versatility. Nearly everything's been done with this baby, and it generally remains relevant even with the Jagermech's introduction. The Jagermech does have better hardpoints in the arms (the firebrand has energies there too), but the K2 maintains its small side torsos, making it a better XL engine mech.
Oh, and Catapults are much more huggable.