I attended VOR last year, and am a long time FG attendant. (My attendance at VOR was business related last year, but turned out to be a lot of fun)
VOR and YT are both great events, and do have some differences. It really boils down to the type of off-roading/exploring you are looking for.
Here was my experience at VOR last year:
VOR last year had a wide range of vehicles in attendance from stock to heavily modified...almost every vehicle manufacturer was represented. I saw everything from built Jeeps, 4Runners, Land Cruisers, Tacomas, a Unimog, a Pinzgaur, a few 4wd Van setups, Land Rovers, a couple sweet Toyota hi-lux diesels, and even a lifted Subaru! It really is an eclectic gathering of vehicles. VOR also draws Moto guys as well. I'd say there were at least 20+ adventure bikes in attendance. In the group I camped with, we had my HJ75 Landcruiser, a built Tacoma, a stock 4runner, 2 built FJ60's, an FJ80 and two modestly built Jeeps. The event itself is held on a farm with primitive camping with just a few porta-potties. I spent both days on the trails exploring Vermont. The first day was spent with the Mountain State Overland team (look them up on youtube) getting muddy and wet. We ran some cool trails (some class IV, but some requiring 33's with a rear locker) and eventually ended up in an old marble mine that was cool. The second day was a bit more mellow, exclusively running class IV roads with a crew from Overland Journal/Expedition Portal and Peter who started VOR. Saturday night there was a huge Chili Dinner hosted by Motus World, followed by a raffle around the bonfire and lots and lots of beer (and whiskey...ouch). Scott Brady from Overland Journal was there and did a talk/slide show about Expedition 7 on Saturday evening as well.
The main difference (in my opinion) is the actual type of off-roading really. FG offers the greatest variety off terrain in the closest proximity, everything from stock class IV roads to the gnarliest buggy trails in the North East. If you simply want to test your off-road prowess and not have to navigate to/on/from trails, FG is your event. FG is simply all about off-roading. Field and Forest is certainly a great camping experience, especially because they have running water and showers. Not to mention, if you're looking for hardcore wheeling, you don't have to touch pavement to access it as it's on the property. FG is primarily a Toyota event.
VOR offers off-roading, but its more of the "overlanding" variety. The majority of the routes are of modest difficulty, though there are a number of trails that are used for the Vermont Overland Trophy that are very difficult (35's, lockers, winch, body damage guaranteed). There are no organized trail runs like FG. Prior to the event, trail maps are uploaded and available for download. Groups seemed to form Saturday a.m. based on what people were interested in, but its up to each individual to decide where to go. Many of the routes ended or break at local restaurants or small towns, so in addition to off-roading, there is an opportunity to explore Vermont towns and grab lunch at a local restaurant. Most of the routes last all day, and will cover miles of terrain.
I don't believe some of the above assessments of VOR and it's attendants are accurate, though I can't speak about past events as I've only attended once. Maybe the event has changed over the years? I had always assumed it was mostly a Land Rover event, but honestly the Rover's seemed to be in the minority. In reality, FG and VOR are more similar than different: Go off-roading/exploring, use your gear/rigs, camp, drink beer with like minded people (and whiskey...ouch) around a fire, talk about gear/rigs, fix your gear/rigs if broke, then repeat the next day.
Lastly, it looks like VOR and FG are on different weekends this year.
Jon