Nova said:
I'm far from an expert, but the last one looks like the best of the three. The advice I'd received was to generally stay away from 1020 steel frames and go with chromoly for the full frame, if possible. It will wind up being a lighter bike while being stronger than 1020. This will add a bit to the price, obviously, so you might find the tradeoff worthwhile to save a few bucks. You will also want to stay away from one-piece cranks, as they tend to be more fragile than three-pieces. I've heard a few people say you can generate more torque with a 3-piece too, but I think they're full of it as that would depend mostly on the length of the crank arms and gearing. Probably not a big deal if you're not going to be trick riding, but still, anything over $400 (whatever that works out to in pounds, I'm lazy) should have one standard. Oh, and you'll want double wall rims whatever you do, for extra durability. Even on just a riding bike, it's nice to not have to worry about your rims warping to shit if you hit rough pavement or decide to go down stairs.
Here's a thread I found regarding gear ratios, 2.75 is ideal on a BMX so you want to be close to that. The first one is bang-on and the last two bikes there come pretty close, so either is ok in that regard.
That's about all the advice I can really offer as I'm no expert, but hopefully it helps. You're not likely to find a chromoly frame bike at $400, but if hi-ten is okay with you then I wouldn't worry about it. The added strength won't be necessary unless you're really beating on the bike, the main benefit you'll be looking for is weight. Also, if there's a dedicated BMX shop in your area (not sure if that Winstanleys is in your area), go in and talk to them about it a bit, my experience has been that they're generally pretty helpful, and they can give you a chance to try out the bikes, feel the weight, etc. More generalized bike shops seem to look down on BMX for some reason, but they also sometimes have them in stock and you can check a few out there. And bear in mind frame size, depending on your height. I'm 5'7", so smaller bikes don't bother me much, but if you're taller, you might find a smaller frame uncomfortable.
Oh, and don't be afraid to buy used. You can get a hell of a deal on a used BMX if you look around, and if it's been well maintained you won't notice much difference from a new bike. Just make sure to inspect it thoroughly and note anything that looks like it would need to be replaced. That's about it.
