Wouldn't mind either really... From what I can gather, space hulk is more tactical, and silver tower is more of a lite RPG ...?
I would go with silver tower, as I haven't tried it yet, I have played an old version of space hulk though, and it was quite good.
I was lucky enough to get my hands on the original print run of this version of Space Hulk- it is super fun. You can even run it as a D&D lite style game as someone as the 'DM' (Genestealer player) with the other players each controlling one of the brave space marines (AKA lunch). Absolute riot to play, especially if you're a fan of the Aliens films. Nothing quite matches the frantic look on the Space marine players' faces as a Broodlord is hurtling down a nearby corridor. Also the flamethrower is the most satisfying flamethrower in any tabletop game, without a doubt. Damn I love the smell of burning Xenos in the morning.
I have space hulk and It´s real fun. Just played the first mission and space marines always loose . The only problem is that it´s for 2 players, though now that @InfamousBeany said it can be played as D&D, I see it more playable, or I could just divide by squads for a 3 player game .
I had silver tower but sold it we just didn't get into it. I will get space hulk as I used to play the pc game and loved It.
I'm more of a Fantasy person than sci-fi, so Silver Tower is up my alley. Plus, the RPG-lite aspect makes me interested, similar to Descent. I will probably get it at some point, but only when it's on sale. It's a great deal, but if my gaming group isn't interested then it's just hobby painting.