My perspective is as follows. There are multiple categories of events:
1. Own organised (e.g. Henrik/Ralf model)
2. Open overtaking rules - RSR/Pistenclub/RMA
3. UK (ATDO) overtaking higher end - Goldtrack, Silverstone, Circuit Days
4. UK (ATDO) overtaking lower end - Javelin, Lotus on track, MSV, etc.
The cost to participate are 1. highest to 4. lowest.
If you are an experienced tracker in the upper quartile of pace then 1 and 2 will give a little more free running. 3 is not too bad for pace but you may need to wait until the last hour of the day to get a totally uncompromised lap (should you be wanting one)
For the UK guys there is another key distinction as well - most track insurance providers will only insure your car on 3 and 4. Some of the more specialist insurers may provide cover for 1 and 2 as well (actually getting insurance cover for 1 is probably easier than 2) though it gets tougher.
I tend to mainly do the bigger circuits - Silverstone, Spa, Ring - and therefore less time spent with MSV and the like on other UK circuits.
I tend to want track insurance cover so will rarely do one without. Overall though, for me the primary decision is usually the date. Which TDO has the circuit you want on a convenient date? ...secondly, which one are your mates going to be at? ...and thirdly, do I know the TDO such that I can call/email them to get me on even if they are showing booked.
...so I will usually book Silverstone, Goldtrack, RMA, Circuit Days, Destination Nurburgring.
...and only where the date is super convenient Lotus on Track (for Spa), and I have done Javelin before (for Spa). With these two mainly because their dates coincided with a back to back date for another TDO at the Nurburgring.
In terms of which TDO has fast drivers, lots of red flags, etc, I just find they all have good days and bad days - it's almost random. So we will all carry with us some baggage of which TDO had a bad day. However, I don't have enough experience about the European organisers (RSR, Pistenclub, etc), Henrik and Ralf suggest they don't have bad days
Finally, there was a time when category 3 (Silverstone, Goldtrack, plus also RMA) used to have higher prices to encourage more 'expensive cars', less traffic, etc on their days. To be honest I am not sure there is much difference anymore. With the growing market for trackdays they all seem to be merging into one - with always a fookin radical causing a red flag! or a trail of caterhams parking themselves on the apex