Just got a XDm 3.8 45 compact last Month and am very happy with it. I have big hands so I put a pearce grip extension for the 9 round mag and put a set of truglo tfo's on it. Feels great in my hands, I do most of my range time shooting at 25 yards and it is just as accurate or I shoot it just as accurate as my 4.5 XDM 45. I also like Glocks so it comes down to what feels good to you and what you shoot better JMO... XD's & XDM's feel better for me but you should try both and do what is good for you.
I just picked up an XDm .45 but I chose the 4.5 because my carry is a G23 or G26. The XDm replaced a G21 gen 4 that I had ejection issues with, but I also didn't like the grip. XDm just feels better in my medium size hands.
I have an XDM9 and an XDM40 (both 4.5). Both feel good in my hand. Had a G22, good gun, but it did not seem to feel as good in my hand as either of the XDMs. A Glock with the changeable backstraps might be better, but I will stick with the XDMs.