For the last four projects, we've been using Swift exclusively. I really like it. The syntax feels modern to me (subjective, I agree).
The compiler however still needs a lot of work. I feel it's quite slow. It's somewhat better where it won't recompile related files when you make one change. But I was used to the Objective-C compiler. That thing _flies_. On a MacBook Air, three years old, I am able to work on pretty big Objective-C projects.
For Swift, that's simply not an option. Especially if you use mogenerator and Core Data (for those not in the know, it's a object layer on top of an SQLite database, and mogenerator generates two class files for every table), our last project ran into about 200 class files. Compiling took minutes.
Things have gotten better. Especially if you're able to put parts of your projects in modules, it's really much better. But still I feel the Swift compiler requires a speedy quad core CPU. If you can afford it, get whatever top of the line quad core Apple offers.