Signal strength is much better than my Galaxy Nexus. In my office building my GNex pulled in no signal at all of any kind -- voice, data, nothing. My brand new Droid Maxx get at least some 3G most of the time, and in some parts of the building I have a couple bars of 4G.
In fact, that's part of the reason I bought a Motorola phone this time, as appealing as the S4 looked. My GNex melted down irreparably about 2 weeks ago, so I had to pull out my OG Droid until I bought a new phone. I was astonished at how strong the Motorola signal was, how loud the speaker was, and how well the battery performed. Those are pretty important features to me, so I sprung for the Maxx. Three days later, seems like a good choice.