if you can, save up and get Trials Evolution. Trials HD is great but it's extremely, extremely, extremely difficult with a very very very steep learning curve. A lot of people don't even get through 1/3 of the game because it's difficult. Plus, Trials Evolution has taken everything that was good with HD and made it so much better. It's much more fun. There's lots of free content. There's online and local multiplayer. You're no longer stuck in a drab warehouse. And its difficulty curve is much flatter. If you want the sadistic levels, you still have them but you can enjoy a lot more of the game before giving up than in HD.
I think if you start off with HD and hate it, you won't go on to the much better Evolution. It's like people who hate Assassin's Creed 1 and won't go further to AC2 and others.
^THIS! I love the hell out of both games and DLC but if you have to choose one then definitely go with Evolution. It's an awesome sequel that fixes the few complaints from the original and adds some nice features.
I picked up Dust and Deadlight after playing both trials. I was going to wait on Deadlight but with Target points I can spend the extra couple dollars and not feel bad. Plus I think I'll play it soon rather than wait and feel bad if/when it drops to 400 and I haven't played it by then. The Hybrid beta was fun and I almost bit at $5 but I know I won't play it much and prestiging 5 times for an achievement is a turnoff.
Now I'm just waiting on the Borderlands 2 Season Pass and free TWD episode and I'm set. I'll just wait to rent TWD on 360 and PS3 and play through the disc once for each.