I know this is old, but I just wanted to add my info in for anyone that needs it. I went from a GS3 to a Maxx HD and have to say that the ability to make and hold phone calls isn't even comparable in areas where there is anything less than excellent signal.
The dBm, IMO, is a horrible way to measure how good of a signal a phone has. Both phones at my house measured the same dBm. I was lucky to get a long lasting call on the GS3 without it dropping and almost every call would break up. With my Razr I have had nothing but crystal clear phone calls, and the same goes for a ton of other places my GS3 had issues. What was weird was the 3G reception on the GS3 was damn near as good as the Razr. I use my phone as a phone a lot though, and it's my only house phone, so there was no way I could live with the GS3.
That said, I'm pretty sure I'm going to roll the dice and pick up a used GS4 when I can find one. The Maxx HD and GS3 have the same processors (more ram on the GS3, I know), but the two are on totally different levels of speed IMO. That, along with the fact that the new Moto phones no longer have expandable memory (my Maxx HD has a 64gb card that I put to use), AND they are coming out with what IMO is last years hardware, is why I'm going back to Samsung.