I started out with a cheapish Topeak frame bag, they are relatively well made and a good price. It lasted only three years of moderate use though before the zip went, which is a major weak point of these designs, with a broken zip it's next to useless. If I lived in the UK I'd probably have sent it off to Alpkit to repair it.
I decided to invest instead in a new Apidura frame bag, much more expensive at nearly double the Topeak one, however, the difference in quality is really noticeable. Firstly it has many more mounting points, which admittedly is much more faff to mount, but unlike the cheaper Topeak, it really keeps it shape, no matter how it's packed, which helps prevent any rubbing on my legs. The overall quality of the materials is much better as is the zip and Apiduras customer service is top notch.
Apidura also do a nifty frame fit sizing tool, upload a side on photo of your bike to their website and then you go through a couple of easy steps to size your bike, then you can trail fit any of their range of frame bags to see which one works: