I have a QSX+ and 3 uBITX transceivers (as well as a Hermes HL2) and would say that they are comparable, with maybe a little more sensitivity on the uBITX. As stated earlier in this thread, the 2.7kHz bandwidth of the uBITX is a real shortcoming for CW, at least as far as I can tell (I am not really a CW operator). Other areas that need improvement on the uBITX are the transfer from RX to TX and back as well as the offset that is in the stock software (the transmitted frequency is offset as an SSB rig would, rather than be the actual frequency of the transmitted signal). You will need to change the Raduino Nano software to fix those issues, but the software is free thanks to open source contributors like Dr. Lee (KD8CEC) and Reed N.
The one really big difference is that the uBITX covers all bands, 80 - 10, The QSX+ is a single band, so you need multiple to cover the same range. Another is the QCX+ is full break in, the uBITX is semi-break in after you fix the software issues.
If cost is the most significant factor, the QSX+ is $80 vs $209 for the uBITX full kit (both with enclosures and excluding shipping).
As an all-around radio, the uBITX is a better deal, however, there are potential issues, as you can tell if you monitor this reflector.
It is really up to you to work out what you want from the rig, how much you want to spend, and if you would be up to troubleshooting some of the problems of either of the rigs. I could not decide and enjoy building, so I have both ;-)