The choice won't matter, any issues will be resolved.
However, I strongly recommend Windows 8 64-bit and buying Start8 ($5) to avoid the new interface if that's the problem.
Windows 8 has many improvements under its hood over Windows 7. Start8 makes W8 essentially identical to W7 in usage.
I've been using W8 plus Start8 for a year and prefer it to W7. It's not much different but it's been rock solid for a year. I always had issues creep into W7 I couldn't resolve aside from Reinstalling and I consider myself far above average in resolving issues.
You are also going to see support for certain things creep into W8 that don't support W7. Already work on DX11.2 is progressing that only supports W8 (a minor issue so far but just an...