The Ultra/Maxx and the X are the same hardware in different form factors. I cannot believe that voice quality is any different. Perhaps the people reporting bad quality on the X are covering the noise reduction microphones while they are talking? Voice quality on my Maxx has been fine. Nobody I have talked to has mentioned anything about not hearing me well, and I have heard others just fine, except one call with my daughter when she was riding on a bus and probably going through varied cell coverage.
As for updates, who knows, but - again - the hardware and software is the same, with the exception of the Droid garbage on the Droids, the different ringtones, and some minor differences (Droid Zapp and the Droid control center widget on the Droids, unlock with NFC on the X; bloatware is different, but that has little to do with updates). If you are waiting for Moto Maker, by the time you're ready to buy, you'll see if the X has had the update on Verizon that all of the other carriers have had already (ahem) before the Droids get it, or if the updates are delivered reasonably close together.
If I were to venture a guess, the X will probably get updates earlier - it is Motorola's flagship phone, while the Droids are made under contract exclusively for Verizon. It'll be interesting to see.
I'm not sure why you are worried about the SIM tray. Are you planning to switch SIM cards often? And, both have SIM trays... are you worried about the volume buttons having issues? So far, mine are fine. (I've had my phone seven weeks tomorrow morning.)