Dehah

I would have to say it all depends on the type of class you play.

As a wizard I pretty much know what I'm going to do long before I do it, as such mouse clicking is my preferred habit. I can queue up my abilities and mouse over others to check the recast timers. Can't check recast timers if you don't use a mouse, unless you have a UI mod that has a numeric display in the hotbars (if you do, link please!). Other than spamming my two deaggros in the event that I unexpectedly pulled aggro, it is not often that I have to do something that requires less than a split second response.

On the other hand, if I was a healer and had to cure the MT, I would probably use a combination, but keyboard would deffinitely be important because my casting order would probably be highly reactive to the current situation. I could be wrong though, my healer alt isn't even level 20 and I don't really plan on playing it too much.

Ravenne

The only time I use the mouse to click is when I am buffing, because those spells are on my 4th and 5th hotbar. I also use the mouse to change camera angle or stear when I'm moving around.

During combat, pointing, moving the mouse, finding the right key, and clicking all take WAY too long.

It's not terribly difficult to remember the order of two - three bars.

Gage

I always use the mouse except for 1234 and that's because anything after 4 makes me start using my hands and then I forget to cast ae avoid and Ishbu yells at me and then I cry and the screen gets blurry so then I get in even more trouble, so ya.

Mouse for the win.

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Ily

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Sqee

QFT - if i tried to play a healer on my set up.. i'd be screwed... my necro is bad enough.

Gustavin

Mouse