First of all, I would put no stock in the numbers. ASU stands for Arbitrary Strength Unit and I think that's just what it is. Arbitrary. And the dBm numbers are useless unless you know that the phone components that are measuring signal strength have been calibrated against a known (or at least the same) standard. Besides which, if you don't know what tower you're connected to, the numbers REALLY don't matter. If two identical phones are side by side and getting 12 dB difference, it's probably because, for whatever reason, they are connected to different towers.
The only REAL test is whether you can get a signal. And for that, my brother and I are both not having good luck with our S4s.
Reception for voice calls seems fine. Our problem is 4G LTE reception.
I have an S4.
My brother has an S4 (personal) and a Note 2 (work).
Our dad has a RAZR Maxx and a MiFi hotspot.
All 5 devices are on Verizon.
At our dad's house, the RAZR and the Note 2 and the MiFi all get 4G signal (but only 1 - 2 bars) and stay steady on 4G, never switching over to 3G.
But, my and my brother's S4s both occasionally switch to 4G and then usually switch back to 3G within a minute or so.
I spent almost an hour on the phone with Verizon Tech Support on last Saturday. We shut down both S4s, pulled the SIMs, and the guy manually pushed a new PRL to both phones. He said the 4G phones are supposed to auto update the PRL every time they power up, but sometimes they don't actually do it. We powered our phones back up and they were no better.
I went to a Verizon store yesterday and got my SIM replaced (even though the one I had was already one of the new NFC ones and only a week old). Then back to my dad's. The 4G reception was no better. My brother's SIM in his S4 was one of the older non-NFC ones, so that's not the problem.
I'm seriously thinking of trading my S4 for a Note 2 now.