The second sounds more human and clear but, are you looking for that with your mascot?
These are the tips I read around these forums of how to improve a recording that I can remember:
-MOST IMPORTANT: Do the oto after the voicebank is done. The best voicebank of the world is going to sound very bad if the oto is badly done.
-Wrap a tissue, kleenex, etc around your mic if you breath too strong to it. Don't eat the mic, farther of the mic may end being better quality. Just test different settings.
-Don't use OREMO except for soft voice. It seems OREMO hits a bit the quality (but I hadn't made an official test, yet, so I'm not sure).
You can use other programs like Audacity, Reaper, etc.
Also, I know Audacity has a "Noice Removal" tool. If your mic has high static noise you'll need that.
-Use monaural with 44.1 kHz. Monaural is needed. Not sure if going to the super 48kHz or even the omgpainsize 96KHz quality is going to help much the quality or if they even work with UTAU. But don't try the lower 22050 Hz except if you want a radio sounding UTAU.
-Try to record all the samples with the same pitch (with exceptions like breath sounds). That way the range is more global (for example imagine you sing "a" in C3 and "e" in C4, then you can't do it right over C4 because "a" is too low, neither under C3 because "e" is too high).
Using a similar volume may help but I'm not sure if just with a clear enough volume is enough.
-Try to record each sample with a constant pitch. Things like AaAaaaA are not easy for UTAU to handle.
-With longer samples the longest notes will sound more natural. But I think to record each sample with a constant pitch is more important so don't them too long that your voice starts to vibrate.
-Record your voicebank under a blanket to avoid external noise and echo. It seems to work really well. The best option is to use a professional isolation booth if you have one!
-After doing the voicebank, and the oto, check if each note sounds ok within a melody, low/high notes, short/long sounds, etc. If you hear an imperfection, like a click noise or breathed too strong onto the mic, just record that sample again. Normal people can't make it the 1st try perfectly.
This process can be made the same time you're recording the samples, of course.
-Take it easy. Don't try to record all the samples too fast or your voice can break.