What happens when someone engages you at range?
RUN AWAAAAAAY!!!
Lol nah.  I'll probably carry a balanced set of weapons (in Halo Reach, I prefer DMR, AR, and Sprint [or their Covenant equivalents] as the most flexible and mobile loadout).
Like I said, we'll see more about the weapons later.  Right now, it just looks like the Medium build is the flexible enough for a healthy variety weapons, tough enough to outlast Light characters in a shootout, and mobile enough for decent SMART to get me to objectives and combat areas.  
Flexibility is my goal in a lot of games; I hate to specialize in one area and be poor in another.  I'd rather be a jack of all trades, master of none.  The ability to switch classes on a moment's notice in Brink helps a lot with that.  I like being able to perform any role in a party; it leaves my teammates/party members to be free to play to their own specialities and I can pick up the slack whenever, wherever it's needed.  (In the MMORPG Dungeons and Dragons Online, I'm a multiclassed Elf ranger/rogue/fighter: I can serve as a high DPS combatant, a skilled sneak/spy/ambusher, a trap-detecting and trap-defeating engineer-type, and I can also see hidden doors and enemies.)
In Brink, I think Operative will be my default though; it sounds like the most fun and most rewarding, and the class that plays most towards my style.