Because I'm a professional tattooer and needed loupes and microscopes for checking tattooing needle points I already had a Bausch & Lomb 45x stereo microscope. Bought it used years ago. I've got various B&L loupes in 7, 14 and 20 power. These are top of the line 'Hastings Triplets'.
After I started honing I bought this 30x eye loupe from Widget Supply
here. Good loupe for the $ AFAIC. Some guys like those Radio Shack variable power hand held illuminated (LED) microscopes that go up to 100x or so. I didn't like the one I got at all with the inverted image and difficulty focusing. One thing I know for sure, the lower the power I use the better my honing looks. ;)