243a0200_ne_Arena_Strategy___Blue_is_Me__Advantages
[Name] Maraider / Hybrid Destroyer [Disadvantages] Not as particularly effective at doing these things as Devil dogs or Immortals. Weak against anti bio units such as Devil dogs or Warp zealot. [Advantages] 
Both these units can attack ground and air, except Maraider is good against bio units with splash damage, and destroyer against armored units. Relatively inexpensive.
Starcraft 2: Marine Arena Strategy | Blue is Me
Advantages