My wife and I have had Vamo V2, V3 and we both have V5s now (5 between the 2 of us). We also had a MVP V1. The MVP died within three months. The Vamo V2 started having button issues after 5 months. We both have a V3 and a V5 each.
We like the Vamo because it is smaller (particularly when using an 18350 battery) and we can replace the
batteries on the fly (along with the benefits afforded by changeable
batteries).
I decided on purchasing a Vamo V5 recently because of my experience with my V3. I was fishing on a stream and the Vamo fell out of my vest pocket and landed in 1 foot of water. I quickly got the vamo out of the water and removed the battery. It was working like new 12 hours later.
The MVP was purchased for my wife. She wanted an external battery that could charge her phone when needed. The MVP is the only mod that I am familiar with that advertises this feature.
Both are great
devices and I enjoy(ed) using both, but it comes down to the features you want. That being said, I've found that I look at price and "bang for your buck" because I know something new will come out in a few months (or should that be weeks/days).
PS - I offered to get my wife another MVP, but she wanted the vamo because of the size.