I run a mixed group similar to your group 1.

HEALER - I haven't really tried a druid or shaman healer, but I find the AOE healing with my cleric to be awesome. It makes like so much easier to just spam Holy Nova (with rune), especially when the shit hits the fan. However, ultimately it would depend on your entire party makeup as multiple elemental shaman have been proven to work well. AOE heals are the key to making things a bit easier here though IMO.

TANK - I find warriors to be very boring. I don't know what it is, but I never enjoyed playing a warrior. I'd go with a paladin or DK or druid as your tank. They offer more to the party and tank just as well. With the upcoming defense changes [I believe they are changing somethign in 3.2?? don't recall what exactly] I am not sure what the does to the druid tank though (if anything).

DPS - Any ranged DPS will work. The main issue here is if you want to have different classes for later. WIth dual spec this is even more of a consideration. If you only care to do 5-mans and not really care about having a choice for a raid toon (assuming you will solo raid) then anything will work. Another consideration is buff stacking. Some of the largest benefits of one class are offered by another class and don't stack, so you may not want both of those classes in your group (I wish I had a good example, but can't think of any off the top of my head).

Melee DPS - I am sure it can work. I think combat would be really annoying though due to the way follow works. Not sure about a rogue. Never really played one, but don't they need to be behind the mob? I suppose you could just engage with your tank and move the mob to the group?

I can't imagine why you couldn't do all 5-man content with a holy trinity group (tank, healer, 3 DPS) or a tank + 4 shaman (4 SP might work too? whatever DPS class that can still offer decent AOE healing should work). It really won't matter what classes you pick in those cases. You can make it work.

Also multiple classes of the same type is not easier to play than mixed classes. I hit one or two buttons in combat, which would be the same two buttons if I had 4 shaman or 4 different classes. Only the initial setup and maybe some noob quests are different.

Anyway, I would just make both groups and try them out for a few levels. How you interact with your party and do combat won't change much at later levels so you will at least get a feel for how an all melee group would work relative to the ranged DPS group.