Probably depends how you multibox, how many different classes you bring along at once and how many spells you need to map keys to or if you prefer 1-button solutions with castsequence macros.

I just got my X-keys pro last week and it is great, still getting used to the layout...I would recommend it over the G15 (which I also have) mainly because they no longer make the original G15, the v2 is a POS. I tried one, the screen doesn't move, the colors on the screen are orange and dark orange (not black like the picture), most of the "G-keys" are gone. I had gotten 2 v2G15 keyboards, one for me and one for my wife and one of them had a faulty W key which would stop repeating when being held down. It went back to the store. The second one ended up going to my stepson and so far the keys seem to work properly but when this original G15 gives out I'm going smaller and probably non Logitech.

So if you have the original 18-key G15 and get used to the G-keys if it dies on you you'll be relearning where your keys are.

Also, I really like the feel of the X-keys pro, the keys feel like they are going to last a long time.