My first Space Marine army was the Salamanders, as long ago in 3rd edition I played my poorly-assembled-and-painted Eldar against a fully tooled-up Salamanders army, and that was cemented 40k as a hobby for me. I would continue playing the Salamanders, but trying to get a really good fiery green is driving me to uncouth words and deeds, so I have been in the process of swapping over to:
The Ultramarines 3rd Company, a.k.a. "The Scourge of the Xenos". The have a special dislike of Tyranids, to the point where their Company Banner features a Tyranid head impaled on a sword. For me, the 3rd Company offers a wide range of modelling opportunities by incorporating bits of their defeated foe into their armor; currently my Captain has a Storm Shield made from the topplate of a Carnifex, and the Company Champion has a custom shoulderguard mounting the head of a slain Tyranid Warrior.