If you were to switch to one character....

[Harrypott]

Used to raid mainspec resto druid, off spec tank. Was awesome, would heal in raids with occasionally tanking, and always tank the random daily since it allowed me to go fast. No wait time etc.

[Ughmahedhurtz]

Tough choice between pally and druid but I think I'd go druid if I went back to solo. They excel at all the same roles as a paladin but they also get stealth and instant flight form.

[Iceorbz]

I picked up a priest - and for raiding was Disc / holy, since some fights are more AOE based and others I would MT heal or something. Your sick in arena's, and will be more offensive in cataclysm then we are now.

You can go heals / dps, which alot of raids and guilds want constantly to fill roles. There are always more spots for healers then there are tanks, since almost all raids are balanced around 3 tanks 5-6 healers and rest dps.

Paladin though, your great in arena too... you can do melee dps and tank, but I don't think they are as diverse as a priest.

[Slats]

I dont mean to derail your thread, and I fully respect your reasons for going back to single boxing - but I see its quite a trend and for some very active boxers here.

I did what alot of you are planning to do back at the start of Wrath. I tried to play my Paladin and 4 Shadow Priests and it just didn't work well, I got disheartened and went to single boxing for many months before levelling up 4 shamans when you could level through PvP and had a geared out tank. I remember heroics where not easy as I lacked hit and other things, but my tank could take a beating.

The one thing I'm most excited about Cata is the new challenges to overcome as a boxer, and to be doing it on day one - to have to learn to effectively use CC, to use the advanced features of ISBoxer or JMB to their fullest. To be one of those people beating the content at its current Tier, not coming back in 6 months later or waiting for the Niley's and the youtube videos or to overgear it.

I'm looking forward to discussing and debating over strategy and makeup in the PvP and PvE forums and seeing these forums come back to life and hopefully show a bit of their former glory from the older days.

But to your original question if I had to pick one thing, I'd pick the same thing again:

I'd suggest Paladin because I'm biased and originally when I started boxing back in TBC, I wondered why I'd never played one before and it became my main and always will be.

[Mooni]

If you do plan on doing this, and plan on doing so permanently, I want to share some GOOD NEWS:

1) You can still transfer characters from the dead account to your main. Boom, incoming handful of level 80s if you want them.
2) If, like me, you only bought the "Celestial Steed" or other fluff on your main account, once you transfer your alts to that main account it's now available to them. Forever. (I was only transfering to claim an X-52 touring rocket, but BONUS)
3) If you change your mind later and want to go back to multiboxing, you can transfer back and keep the goodies.

That was my experience, and is of course always subject to change according to the ESRB warning.

[Siaea]

Mage. When I play solo, my mage is king. Most fun in PvP, and people love when you make them dinner.

[valkry]

Druid feral (tank)/resto duel spec. You can heal and tank and that tanking spec also does respectable dps in cat form.

[Vicker]

I seem to be outnumbered, but my vote is for prot warrior.

I would say if you're going to focus on a single character, you should also focus on a single role as well. My favorite role has always been tanking, and my favorite tank has always been warrior. Given a choice of tanks, raids always like having a warrior. Sure, other tanks can do everything just as well, but a lot of people still subconsciously associate warriors with the pre-WotLK days when the best raid tank was a warrior, hands down.

I also find the warrior tanking mechanics more interesting than the other tanks, but that's just me.

[heyaz]

mage or warrior

[Simulacra]

Pally Tank / Lock
The lock is my achieve junky with max fishing/cooking, and is reasonably geared. The pally is my "other" main. I would take both but if forced to choose just one, it would be the lock everytime, there's just something uplifting about draining someones soul. Mwahahahahaha!!!