Group selection. I'm torned!

[Redbeard]

Also... nerfs and buffs come in waves. Youre going to be chasing after blizz constantly if youre going for a "power build".

Go with class (s) you truly enjoy. Maybe make a theme for your team and stick with it.
Start with a tank and a healer and go from there. When you vastly outgear your content you can even loosen those requirements a bit.

[Drommon]

I have a warrior, priest, mage, warlock and druid team (80x2, 77x3). They cleared instances at their level with practice. It wasn't easy but I was determined to see them through. With practice I was able to succeed. I agree with what Redbeard is saying, a power build will be more likely to get nerfed. I am waiting for blizz to nerf pallys into oblivion as my pally build (prot, holy and 3x rets) is stupid powerful. Ideally, play what is fun to you. If you want to be succesful in heroics then build an AoE tank and strong healer. The dps can come from anywhere but there are some easier choices. In my humble opinion, the pally tank and shaman healer is the combo that can take any 3x dps and make it work. The reason why I have a warrior tank in my first team is because I love warriors. IMO warriors and druids make very bad tank options for boxers. They can work with practice though but you will spend some time being frustrated at first trying to make all your toons synergize correctly.

For PVP - 5x Shamans and 5 Paladins do very well.

For both PVE and PVP - 5x Pallys do very well. Although I don't have any experience on this but I will echo what others are saying about DK + Retsx4.

Good luck on your Team.