Silf, I'd definitely recommend doing research before buying your first mech with your free hawken points. Test drives and reading meta game commentary on balance and gameplay and stuff on the Hawken forums would probably be the best option. Youtube videos can also give an idea of how a mech might play, but the videos can be outdated.
Don't do an impulse buy like I did. You're basically paying with free time, and spending the free points on a mech that you find out you don't like or that's underpowered, niche, or whatever, would make it way less fun and more grinding to get enough points to make a better purchase.
Also, Raider at the moment is meh. From my experience, an assault or just the recruit works better. Raider's secondary takes 4 seconds to reload, making a missed shot painful, the primary generates heat pretty fast compared to machine guns, and the skill takes 60 seconds to cool down for 10 seconds of speed. Not as good as berserker's pure damage or assault's heat-sinks or bruiser's damage tanking that only has a 10 sec cool down. Raider could still be really good, but from my own experience playing on a relatively poor performance computer, it's not as easy to play as an assault mech.
If you had to choose between raider, assault, or berserker, I'd recommend an assault or berserker over the raider until it gets some changes. I played berserker in beta, before there were various changes such as the hud and mech health changes, and berserker was fun. I actually had worse FPS then, and still had fun with berserker. Raider feels like a chore to play and half the time I feel too weak to actually fight an opponent. Berserker is basically an assault but lighter, faster, and more airborne.