Out of all the founders mechs, the Atlas and the Jenner have the best hardmount/weapon configs which work (*as currently balanced*). The hunch "could" be good, but not unless it gets a clan XL engine (assuming you will even be able to do that), or clan double heatsinks and ferro-fibros armor is out. Otherwise it is too slow, too squishy, and/or too out gunned.
The Cat is "ok". It isn't the Cat that people will be using as it isn't the K2. Unless they fix heat or heatsinks, it is useless.
I love the founders Atlas. You live and die by your team, but you should be taking 2-3 mechs with you when you go if you are playing right (i.e. you learn to shoot the head or learn to recognize which mechs are probably using an XL engine and shoot their sides). What you don't do is stand there and shoot dead center on a mech (this goes for piloting any mech, but more so on the Atlas since you should have the firepower to blow off a head in 2 volleys). So if you spent more than 8-10 seconds shooting at a mech in an Atlas, you spent too much time.
The Jenner sucks until you get a 300XL engine. I would not even bother using one until you do that, so that means lots of matches getting creamed until that happens if all you get is the founders jenner. I personally plan on using the founders atlas until I have enough to purchase a 300XL engine, which has the side benefit of being the best engine for the Jenner, Hunchback, Raven, and Atlas (if you don't mind having a squishy Atlas). But WITH the 300XL, it is (in my opinion), the 2nd best mech in the game (the Raven with the 300XL is the best). Why do I say it is the best? Because you don't need to rely on your team to survive. You are faster or as fast as every mech in the game so you can simply run. Because of your speed and size, you can take cover just about everywhere and only take minor glancing hits from lasers. If you pilot it correctly you can get behind every mech in the game and core their weak rear armor. I have a round where in my Jenner (it wasn't the founders, but it could just as easily had been), I had 7 kills and 1 assist with many of those kills being 1v1.