First off congratulations on moving up to 6! It's the gateway to having 12 or more lol.
Serious note here. I have played the group I enjoy for many years, I dropped my bard a few years ago, swapped for a ranger. Why? I just love bow damage lol.
Anyhow, my normal setup Necro, Mage, Enchanter, Sham, Druid, and Ranger. So, I've yet to have the "need" for my Ranger to tank anything, but she does have Augs if need be. The mage pet is generally the main tank, I drive my necro, do all the pulls ect.
Through progression into harder content, I have realized, you can do it with pets, but a few requirements are needed. Obviously the best EM earrings you can get, but honestly having two healers is a must. My Sham is my main healer, but him and my druid both dps also. Heals come first always of course. But, I find my pets spike a lot and generally take a lot of damage.
So, I spent a little time getting a paladin up and geared. I just like paladins, just require that special someone to shine! I noticed right off the bat my group was doing a ton less of dps without the necro, but my healers weren't healing as much.
But, when you look at the downtime ect, the mage pet actually was an improvement overall. Now, when I moved into harder instanced content, well.... My pets were basically useless, thus the rain of the paladin. Even though the dps is less, I can cruise through content easier. Also, I dropped the druid, and put a necro in, I just cannot help myself lol.
Next group setup I plan to do is. War or Sk (leaning towards War), Rogue/Ranger, Bst, Zerk, Bard, Sham or cleric. I really love Shammies, damn do they shine! But, I've not really had a cleric in my group past Omens, so something for me to think about. Also, not had a Rogue in my group since Omens, so figured might be time.
Anyhow, play what you enjoy. There's always a way to make things work, but in the end, most all of us have a real task these days.
Happy hunting!