Granted my opinion is a little biased as I'm in a torrid love affair with my Provari, but the reason why I believe the Provari is held in such high esteem is because:
1. It's a single battery VV mod
2. It's 100% stainless steel
3. The electronics have been proven to be very reliable over the years
4. It's a US made mod
5. It can take 18490 or 18650
6. The vendor offers terrific customer service
7. It was one of the first mods to display ohms/battery voltage
If you're not into stacking batteries, for whatever reason, be it safety, convenience etc, your options for a single battery VV mod are limited. The Lavatube being pretty much the only other contender in this field, while it may have the same functionalities, the two are miles apart when it comes to build quality and reliability (you rarely hear of a Provari's battery connector popping out).
Then again there are a lot of PVs that have cult followings, take a peek in the GG forum (ask Martinc, he knows a little something about that

), or the Notcigs Buzz Pro forum, or the Reo forum.
Just as with anything else, to some people certain things are worth paying more for. Why pay $50k for a Lexus when you can get a $20K Ford - quality, reliability, and performance.
**End proclamation of love for Provari