I've been diving the Dimension i3 since January and love it. It is extremely comfortable. I also dive a Hogarthian BP/W setup and a Zeagle Ranger LTD depending upon the situation (demonstrating, assisting, fun-diving). I had a chance to check out the Axiom this week at my LDS. It is a very nice unit. Streamlining is about the same as the Dimension. The right side drop down pocket is larger and more usable than the Dimension. The Axiom has a left side pocket that the Dimension does not have. Left side hose routing is slightly different and somewhat improved on the Axiom, in my opinion. The Axiom has an additional stainless steel D-Ring on the right side, which is a welcome addition. A big plus for me on these BC's are the Octo-Pockets. Almost every octo-clip I've ever tried has failed at one time or another. I've never had my octo accidentally come free with this system. I prefer the tank band on the Axiom to the Dimension. The tank strap has, "pre-sets," (gaps in the velcro) for different tank sizes. You probably have to see this feature in person to appreciate it.
I like the i3 inflator however, I advise one word of caution here. I do not recommend using the skinny Miflex HP guage hose with the i3. While not a problem with the recommended hose routing, the Miflex hose is small enough to catch underneath the inflator lever and cause it to actuate. On the Dimension there is a velcro flap under which you can route your gauge hose. On the Axiom there is a path underneath the pocket you can route your gauge. Using these mitigate the above mentioned actuation problem.
This is one BC you can b that will work for pretty much every sort of recreational diving you would do. Construction is pretty bombproof, although I'd like to see a little more robust manual inflation device (which does work just fine BTW). If I were to boil it all down to one word for this BC, I'd say that word was, "comfort."
I plan to sell my Dimension and replace it with an Axiom.