For the first few years I was involved in using Vegas it was on other people's projects on their licences. The first version of Vegas I used was the first Sonic Foundry release. I think I assisted on the mix and editing of a drum and bass album. I then used version 2 on another music project (possibly version 2 came out in the middle of working on the first project). I was called in to complete a video project started on Vegas 5.
The first licence I bought for myself was for Sony's version 6. That was probably the most solid version of the software I ever used, and the motivator for going with it was good workflow from the Sony Z1E. I did a load of video projects with that and started a major project which eventually was completed in Vegas 8. We tested with Vegas 7 and found it to be unreliable, but we wanted the 32 bit modes of Vegas 8 and DVD Architect with Blu Ray support. Unfortunately Vegas 8 proved to be only slightly less unreliable that our tests with 7 suggested and the 32 bit modes were next to useless. We were keen to try 8.1 64bit but were tearing our hair out when we realised there was no 32 bit plugin wrapper, which meant that Sony skillfully avoided the biggest and best advantages of working in 64 bit, the ability to take advantage of vastly more RAM. Around that time I got banned from the forum for several years for complaining about bugs.
The next version I went for was Vegas 12. The main motivation for this was switching to 64bit, the ability to (sort of ) use OFX plugins, and some anecdotal reports that the software was a lot more stable.
I am waiting to see what happens with Vegas 15. I do need some features that it offers (for example the new deinterlacing features introduced in 14) but I frankly have no faith in what will appear, and expect the same old routine of it arriving completely buggy, and these bugs carrying through until they are finally addressed in Vegas 16 (maybe). I still can not get over the Dolby Pro AC3 codec disappearing in Vegas 14, and the fact that in spite of promises that it would reappear in an update at no further expense to the user, it seems that this is not going to happen. If Vegas 15 arrives without that capability then I will be getting out as soon as possible.