I much prefer the under arm routing since it is more streamlined and even out of the box you have a longer hose for sharing. It is much more streamlined, and I find it much more comfortable than the regular over the shoulder, I always noticed that with the hose going over my shoulder I could feel it moving in the water column and it was a tad annoying. It seems that with the under the arm routing the reg staying in my mouth easier, it is less likely to be pulled to the side.
I have an older maximus also, and have found it to be the most comfortable reg I have ever used. The moisture retention system does work very well, the change from a normal reg to the maximus was a pretty big difference in dry mouth. One of the reasons it makes me sad that so many regs now have plastic and not metal in them. While I always make sure I over hydrate while diving, I still find the vanes to help with the just the basic overall comfort of the reg.
One thing that is very much personal and probably won't bother or be noticed by anyone else is that for me, when I use my maximus over my SP G250 is that the maximus seems to float a little better off my chin than the SP does. What I mean is that I can feel the SP on my chin sometimes and I never notice this with the maximus. This is not a big deal, but again it is something that I notice, and it becomes a little annoying to me.
The first stage is a very strong design and are pretty well bullet proof, also one advantage that I have seen is that you can get the sherwoods serviced just about anywhere.