Compact and clear - Bausch & Lomb Folding Pocket Three-Lens Magnifier Loupe 81-23-67

It's hard to find a better magnifier than this one. In fact, my wife 'stole' mine and I had to buy another one. She uses her's to check for flaws in jewelry. I use mine for technical inspection of aircraft parts.
This unit is small and easy to keep on your person, so it's there when you need it. It's clear and helps show great detail. The lens is small in diameter though. Weigh the benefits of its compact size against how large a field of view you'll need in whatever you're looking at.