I recommended gemming stamina and resilience because that's what an inexperienced player should do.
200 extra haste won't save someone who just stepped into the arena, doesn't know which abilities to expect from which classes, doesn't know how to time his own spells and who doesn't know how to use the sorroundings.
2000 extra life and 100 extra resilience, however, may make a difference in a game between equally inexperienced teams.
Gemming haste or spell power is all about min/maxing, something you won't be doing until you've reached a decent rating (>1500).