I've actually run a few different ones and have finally narrowed it to the most comfortable set up yet.
Started with the BCA Float 30 and a Tekvest underneath. Moved on through a few different BCA Float series bags with the Tekvest underneath and it never felt "right". I also kept having issues with the compressed air cylinder and it would always leak!! BCA was great to work with and they always took care of me, but it was a pain.
Then I ended up moving to an Ortovox Freeride series pack with the ABS system. The pack was more comfortable and the air system had NO issues, which was great!! Only problem was replacing the air system when you fired it off was obviously more money and little harder to come by, if you didn't have a spare with. Overall it was a little more comfortable but still not what I was looking for.
So........
Then came the BCA Mountain Pro vests. I've run the first version, which was good and I'm now in the most recent version. I can tell you this, the vest system is way more comfortable then running a Tekvest / pack combo and is a much "cooler" setup, meaning you have to adjust your clothing. The Tekvest / pack combo has you running much warmer and "I" found myself running much less for mid layers. With the vest, it was back to the drawing board and I ended up increasing the amount of mid layer to increase overall warmth. It took me a few rides to get use to this dialed in and make adjustments, but once I did I've been very happy!
The air systems seems to have improved but again, BCA is great to work with, if you have issues. Plus the BCA air system seems to be the most widely used out west or least where we typically ride.
Other benefits with the vest include the protection, outer pockets that are easy to access, to include a special pocket for your transceiver and its easy on and easy off! They also have plenty of storage for me, but I only keep essentials on my back, so that's not a huge deal for me. If you are the guy that doubles as a "Sherpa" then you may find the Mountain Pro Vests a little lacking on storage.
I guess I look at this way, get out there and try different avalanche air packs, then buy one and then use it!!! There a great investment and can save your life, so get something that "you" like and "you" will wear and don't worry about what all your buddies are running.