I think it will always depend on which one you started with first. They are very different when it comes to editing VSQs/USTs, so often if you're used to one you'll find the other when you start using it confusing, irritating, and difficult.
At least, that's how I feel about Vocaloid. :'D
To give Vocaloid some credit, I've been using UTAU for over 3 years now and I own two very hard to use Vocaloids (Tonio, who I regret buying since it was full price whyyy did I, and Miki, who was in the AHS bundle sale and a good catch but is VERY hard to work with).
But there's lots of things they do differently. UTAU gets the advantage of being free, so point for that. Vocaloid has an interesting method of editing the note qualities with OPE and DYN and such that would be nice to have in UTAU - it's much more dynamic than what we have. Also Vocaloid voices are fairly guaranteed to be high quality, and even when they aren't (initial Galaco, trial Lily) they are still better than your average UTAU.
Now, I feel that the advantages of the Vocaloid software start to die off however when you compare it what UTAU is capable of. Vocaloid will never have scream voices. I highly doubt they will ever get a Kire, a Sakebi, anything dynamically multi pitch, nothing like that. The closest Vocaloid ever got was Meiko V1 (Meiko V3 is still strong but kinda nerfed), though some incredibly good editors can make Kaito and Iroha and such do well. In the voices category I don't think Vocaloid can ever hope to meet the level of quality and variety that UTAU boasts. It may be only 5% of UTAU banks that can do that, but assuming there's 5000 UTAUs (close to 4000 in last official count in last year but that was only counting YT and NND), that's still 250 UTAUs.
We say pitchbending in UTAU is easier because it's quicker to understand. You have a piano roll, and while the notes are the basic area for the note, the lines and portamentos you add directly illustrate where the note will be. There is no guessing, it's right in your face where it goes. A single "a" can go crazy and hit many notes in a dramatic sequence with pitchbends.
With Vocaloid, I still don't understand it well. It's the same basic principle, but don't you have to use PIT (and POR apparently does something? I never got it explained well). And that confuses me. How do I know where the PIT is going when I draw the curve? How far down do I need to go to hit two semitones lower? It feels so tedious to have to place a bunch of a single note to get it to move around because I can't judge where PIT goes.
But again, I'm not very experienced with Vocaloid so it's all very foreign to me.