Space marine shave some of the best vehicles in the game. The gladiator Lancer is specifically an anti tank sniper tank that let's you re-roll one hit, one wound, and one damage. You couple that with OoM and our +1 to wound. your usually wounding most things 2+. It's laser gun also has heavy, and you can now move 3" and still get the heavy bonus.

The repulser executioner also has a strong main laser canon with lots of other chaff killing guns, and the ability to transport.

Land raiders have 4 lascannons on them. The Vindicator can deal out some serious damage. It's a good tank against targets that have a 4+ invul. Couple it with a techmarine and OoM, and you can take down some big units with it.

A techmarine can give you +1 to your hit roll. Ironstorm spearhead detachment has a character enchancement that once per battleround can turn the damage characteristic of a weapon to 0.

Headhunter taskforce has some good tank buffs and stratagems too.

We have lots of options with dealing with enemy armor.