I just bought a Blue Sky, but before that I had the flint. I've also spent some time with the Boss RV-500. First of all, the Blue Sky is about all the reverb I'll ever need. It sounds stellar through the FX loop though can be a bit tricky to dial in at times. I wish I had the Big Sky because it has that extra flexibility to dial in just the right reverb. However, the rest of the fancy options are overkill for me. The sound is good. The Flint actually has one reverb, the 70's reverb, which I really like a lot. It has a great sound, a plunky attack, and just a really good reverb all around. That being said, I needed just a little more flexibility so I exchanged it for the Blue Sky.
The RV-500 is really, really good. I have a Strymon Timeline and Mobius by the way. I've compared the Timeline to the DD-500 before and thought about selling my Timeline for a DD500 because not only did I like most of the delays, it was a little easier dialing in different delays and it sounded better through the amp input. The Strymon stuff only sounds good through the FX loop for the most part. Anyway, the RV-500 is spectacular. There is a lot of configuration options, but it's not overwhelming for the most part. I like the RV-500 with distortion sounds and clean sounds alike. My Blues Sky loves clean tones, but is hard to get just right for distorted tones. Other than that, I still like the Blue Sky spring reverb better than the spring reverb on the RV-500 just a little bit more.
I have watched countless videos and read dozens of reviews of the BOSS stuff. When all the DD-500 vs Timeline videos hit Youtube a couple of years ago, i couldn't make out anything the critics were saying. I think it's mostly just brand loyalty because I thought the DD500 was every bit as good. If you can afford the Big Sky, it's worth it -- infinite reverb sounds. If you get the Blues Sky, you won't be disappointed. If you get the RV-500, you will love it. They're all very, very good.