For PVE I would say magplar for solo content and running dungeons with 3 DPS and a tank. For trials, stamplar is preferred because it brings more damage and group support, but is harder to play iMO.
They are pretty similar in DPS at the moment. I'd say Magplar is however the better pick for PvE, simply because it is much more flexible and reliable.
Magplar is easier to play in pve but in PvP they are more healers. Found it hard to be a dps in pvp without zerging.
Stamplar takes more skill in pve due to main spammable not auto healing but once mastered wrecks everything. In pvp they are solid but just overall crap sustain compared to the other stamina classes.
Edit: if you chose the lizard race, you can switch back and forth from mag and Stam . You don't need a dominant race until you feel like you mastered the class imo