I own both, and for the most part, I agree with the above comments. There are some significant differences worth noting.

PicBasic Pro (PBP) was designed to be a PIC alternative to Basic Stamp 2's. It's very good at that, and its code runs much faster than stamps. It is very easy for beginners to transition to PIC's from Stamps. I've made some good code with it. You pay for version updates.

Proton+ Development Suite (PDS) was designed to be a good PIC compiler, with many commands being Stamp compatible. (They've also added some similar commands that are optimized for your specific use, instead of a "catch-all" command.) PDS has a broader command range, and compiles code much smaller and runs faster than PBP. (My PBP code converted to PDS was about 20% smaller!) The current Beta version, which is available to all licensed users, has many new powerful features, like automatic variable saving for interrupts. (This makes a few of Daryl's add-in code obsolete.) There are three levels of optimization for even more compact code, that can save up to another 15%. For 18F's, both high level and low level interrupts are supported. Plus, you get a development board simulator to test your code in. PDS has a macro capability to make your own commands, and call them with parameters, just like any other basic command. I'm one of those who "switched", and most of what I do is now PDS.

Both forums have excellent support.

And yes, Swordfish looks neat, but it's only 18F's. I'm sure that will change, eventually, but probably towards more advanced PIC's. It's "structured", but that really only has a benefit if you are writing huge code (which 16F's and smaller can't handle). In reality, you can write structured code in PBP or PDS, too; it just looks slightly different.