1 good rule of thumb against melee heavy teams is : get that stoneskin totem down!
Ive tried arena with some different healers, and what i find the most helpfull is COMMUNICATION.
That 1 word "silenced", followed by LHW from all shammys on the enemies target = win.
And "heal, im LoS." or ANY communication is sooo frikking important.
I've lost so many matches because my healer has not communicated problems, 5second silence on my healer is more than enough to nuke 1 of my pants down but not if i know about it.

Also another tip against melee teams, shammy>warrior>rogue and if there are 2warriors start with purge on the first to charge in, then switch target and go all out.
When they start to run, you drop fire novas, then heroism/bloodlust.
The healer ive played the most with knows how to complete my needs from a healer, getting those spellreflects and grounding totems for me.
And having an insane overview of the battlefield (wich i dont have in the heat of battle) and relaying that information to me fast.

A pally healer is very nice, as they are considered tough, but they are pretty easy to lock down.