I'm surprised Canon recommended something that was incompatible! What did they recommend?
All current macro lenses Canon makes should work with the 7D, but saying one is the "best" is subjective. What's your budget? How much magnification is ideal?
Here's a review for the 100mm non-L macro lens that also discusses a bit about different focal lengths available:
The recommendation from Canon support gave me an incompatible lens.
Hello galapshan! Welcome to the Canon Forums! To expand on jfo's comment, any lens that Canon manufactures that is on the market right now is compatible with your EOS 7D. If you could let us know which lens was recommended, and what you intend on shooting, we'll be glad to help you better!
Short answer for performance/price: 100 non L
There is a 50 and a 60 but they are EFs lenses so there is a little restriction with them if you may go FF later on.
If you're talking about the EF 50mm f/2.5 Macro, it's not an EF-S lens so it works on crop and full-frame bodies. It's has some quirks. And it qualifies as a macro in the older sense. Below are links to its Canon description and a review that I found useful before I bought one.
To the original post, it really depends. The different focal lengths are as important as they are on a non-macro lens. The longer lenses have more reach which is useful for bugs that can easily escape. But sometimes you want the size of the subject relative to the size of an object in the background that only a shorter focal length can give you.
I'd go with the 100L.
And immediately shoot 100 bugs to make myself feel like it was worth the price.
The MP-E 65 will go to 5x. That's as much mag. as you're going to get "out of the box". It's pretty highly regarded, I was talking to a guy a while back who went with Canon because of that lens. 😉 Outside of that the new 100L macro is quite sharp and has IS, which can be quite handy. The non L is quite sharp and affordable. Sigma has a 150 to compete with Canons 185mm Macro. The sigma has IS but I've not seen any first hand reviews on it. You can always go to Flickr and search for groups related to each lens for samples, or you can go to POTN and check their lens sample archives.