Yeah I do eventually plan to get all three but until I can get that elusive 100 MSP through the Bing rewards program that Curufinwe linked I want to figure out which maps I should get first. I'll definitely get High Seas then and decide between the other two.
Also, what skills do people here run for Mercs?
Edit:
Good Mercs video on Steel Beast that shows a good strategy for a 150 combo. At around the 8 minute mark one guy posts up at the bottom level and one guy in the middle level, and when they hit the 130 combo the guy on the middle level rushes up and picks off the J'avo that are parachuting in. I need to try this strategy next time I play the game (i.e., once we get power back in lower Manhattan).
Edit 2: Oh snap!
According to this, taunting in Mercs refills your stamina bar quickly. Useful! (The user gives a shoutout to Sectus, where he originally saw this)