I was having a discussion with my friend. What would you say is the biggest and best annual Vegas MTT that does not occur May-July?

Is it one of the WSOP Circuit Events, a Venetian Deepstack Extravaganza? Unless I am missing one, I am not sure there is a clear-cut "best"

The biggest prizepool will be WPT 5 Diamond in December. Nothing else will be close, really.

How is 'best' being defined? Turnout? Structure? Payout? Number of non-NLHE events?

You didn't define "biggest". I quickly glanced through Card Player for every Vegas tournament outside May-Jul in 2016 and prizepool-wise Billy is right, Bellagio 5 Diamond is the biggest with one that topped $7 million.

Runner-wise Bally's WSOP event had one that topped 1200. I found a few other events that topped 1000 as well, but didn't beat Ballys.

Whatever 'best' means to you. I would assume for most people it would be related to prizepool or turnout.

Whatever you consider to be the 'premier' Vegas event.

A spot check suggests only a handful of non-summer Vegas tournaments get 1000+ field sizes. Since August 2016, the largest field size I saw was a $365 re-buy at the February WSOP Circuit stop at the Rio, which had 1498 entries. The 250K guarantee at the Venetian's Deepstack 3.5 had 1420 entries.

I agree there is no clear-cut "best" and everyone has their own criteria. For me, an event is good if it entices me to travel cross country.Typically, the WSOP circuit stops, and the Venetian DSE events which are usually concurrent are the best (IMO) events throughout the rest of the year (non-summer) in Vegas. I try to hit those up in November and Feb/March. The Wynn has also started to put together some pretty decent series in the Fall and spring.

I feel like last year, the WSOP/PH totally screwed the pooch with their September schedule. And then the March Circuit ME was hurt by their bizarre decision to change the ME to Sat/Sun instead of Fri/Sat. The event held at Ballys the prior year was a huge success and proved that you don't have to have a perfect venue to have a great event. Hopefully the WSOP has got their act back together this year.