Prores and DNxHD are really, in my experience, the smoothest codecs when dealing with projects that need to be handing off or back-and-forth. Premiere really does treat most codecs really well and makes it possible to edit just about any of them with little trouble, but Prores and DNxHD can just make life a lot simpler for everyone involved. Of course, with the Mac still be the dominate platform for a lot of video work, Prores tends to be the easiest to get everyone on board with.
I would suggest looking at Premiere, but in the end it really comes down to your preference and your client needs. If you are able to integrate your work into your clients' workflows without any hiccups and deliver a professional level product, then there is little reason to switch.
If you have multiple issues working with client workflows, have to lower your clients' quality because Vegas can't meet something they need, and constantly have to make excuses for some deficit of Vegas, then it's very much time to consider another NLE.
I would also recommend taking a look if you are an editor that works for facilities as contract or fulltime often. It's one of the NLEs that should be in your tool set.
Agreed and I'll add that even if FCPX had never been released and Final Cut had remained more consistent, I still would have switched simply due to the fact that FCP was and will likely always be tied to Apple hardware. This isn't a price issue or even a quality issue for me, but one of flexibility in both my own workflow and in being more able to work with a client's workflow. The terrible product that was FCPX only quickened my switch.