Never buy any without first trying them on, but I can make some general recommendations.
1. DO NOT buy plastic frames (unless they are the DFV Buddy Holly frames because these don't flex [I don't have DFV btw]). Plastic will flex when tightened on your head and cause the loupes themselves to distort unless "just right" around your head. Many of my classmates got plastic frames, and do not like them. In fact, several of my classmates switched brands after bad experiences with customer service and quality from one brand (I'm not going to mention them online).
2. Get 3.5 magnification. Don't listen to the reps. Let me repeat- DON'T listen to the reps. You will want to get 3.5 no matter how much they say, "Oh, get 2.5, it will be easier to learn on 2.5's" . You'll get used to any type of magnification after about a month, but 3.5 will work much better when you really need the magnification.
3. Get a light- but don't spend $600-$1000 on it. The most highly recommended are the Lumadent and the Featherlight Ultralight. Both have great reviews and cost around $365-$400. Both are small and both are durable.
That's my take on it.