I use Microchip MPLAB IDE and assembler under Windows XP / 7 with Pickit2 & 3 programmers.
I use it because the O/S and application software combination works and I don't have any issues with it so I can get on with the developing. The Microchip software is free and always updated to support their products as well as having a good support forum so I see no need to look elsewhere.
Programmer hardware wise, PICkit2 and 3 cover all the Microchip products I'm ever likely to need to use, they work reliably, consistently and are cheap. I have tried some of the 'free' programmer hardware designs and software, but they were too temperamental.