No but seriously GRETA IS BETTER. She finishes the game with more than enough health- almost 150, if you evenly distribute skill points. If you want a meat shield, get Alawn. If you want a capable fighter, get Greta.
Also, if your a good shaper, i suggest you get niether. Fill your party with Battle Alfas or Dryaks instead of Alawn or Greta. They will be a big help on the first two islands though. Carry one to Dhonals Isle, and then use him/her if he/she is needed.
Then again, if you are interested less in combat and more in encounters, they add to the experience a bit.
Greta even helps you convince the rogues not to kill you. I doubt Alawn does that.
Finally, don't you notice that the Rogues and the Shapers are like opposites? Alawns a man, Greta is a Woman. Each game also ends almost exactly the same, just one against the shapers and one with.