I personally want Samsung to make it again. HTC and LG would be number 2 & 3. Moto would be 4. The main reason for this order, the displays. Samsung's screens are arguably some of the best, year in and year out. HTC and LG both have nice displays on their higher end devices. Outside of the OG Droid, I haven't seen a display on a Moto device that has wow'd me. There almost always was something out that was better at the time, subjectively at least.
Moto could potentially bring a few nice things to the table though. No other manufacturer seems to do accessories like Moto. While this isn't a selling point to me, as I haven't purchased an official dock for any of my devices thus far, I could see this as being a nice feature for other folks. It would be cool to have a battery like the the one in the MAXX.
I think we are approaching a point in which the internal specs (processor, GPU, and RAM) won't matter as much outside of gaming and benchmarking. Besides, Google is in on this too, and they have a say in picking components. The N1, NS, and GN each had some of the best, if not the best available in a phone at the time. So this isn't a concern of mine, as regardless of the manufacturer it should have decent internals.
Now this isn't considering the Asus, Acer, Sony, Pantech, Casio, or any other manufacturer that doesn't have a large stable of phones.
Of course a lot of this is my opinion, and to be honest, I don't know if I will care too much who makes the next Nexus as long as it comes to Verizon (on time lol). If Moto does get to make one, I hope they don't get to name the device. They have had some terrible names, either all caps and/or using X's in weird ways. Motorola Nexus XIPPITY-DO-DAH MAXX.