I would say:
1) Start with a CV; this will make you practice the phonetics if you are new into this. CV's are faster to fix if you have a sample wrong than a whole VCV string. Also the number of oto settings you'll need to configure are less and that's less stressful to new users.
2) If you want to add a plus to your CV, you can record VVs. VV (vowel-vowel) are recorded like VCV strings (aaiauea) or dipthongs (ae, ai, ao, au, an). These will make the vowel transitions more natural than the crossfade tool used in CV's.
3) If you already dominate phonetics and you can keep your pitch; go for VCVs. VCV strings can be also used to configure CVs, so you can use one bank for ust's in both methods.
There are mere recomendations... I have seen people who debuted in UTAU directly as VCV banks (Sorane Rana), but I will recommend you to start with a CV to not feel so confused about the program and the configurations themselves.