MMORPG terminology in SWTOR:
*** Dungeons ===> Flashpoints.
*** Raids =====> Operations.

For an easy Impside class to play that will be fairly versatile and reasonably tough, on Impside, play Mercenary and make sure to pick the "Arsenal" discipline.

Both Marauder and Sniper score very high on damage output, but have sharply limited capacity for self-heal, while Mercenary gets less damage output, but makes up for it by being very tough and very capable of self-healing.