MPLAB supports integration with other Basic compilers. I do not think it comes with it. Better check fully. I've seen an older Proton Basic work with MPLAB on one of my older laptops a couple years ago. It did integrate, but had to follow instructions to the letter. As for the compiler, very similar to Oshonsoft but with some differences in how they structure things. Proton compiler code (via MPLAB compile) was extremely similar to Oshonsoft assembly code.
So, when shopping around for a Basic compiler, check that it integrates with MPLAB.
Proton Basic has better support for enhanced features found in higher end PIC chips. For me, the simulator in Oshonsoft was more important (I only use basic 16F chips).
Another compiler is mikroBasic PRO by Microelektronica