I personally recommend FamilyMart for the better quality and price of most things (especially fresh food).
Are the prices really appreciably different between the conbini chains? Everything seems about the same to me. Maybe it’s product specific, like 7-11 tends to have the cheap 7 brand coffee, but Fam Mart and Lawson don’t have their own.
For things like pre-packaged goods (potato chips, soft drinks) the price will be almost the same across all convenience stores.
But for the fresh stuff (sandwiches, bento, fried foods, etc.) 7-11 is charging noticeably more than everyone else. And after 11 years, I prefer the quality of the stuff I find at FamilyMart. They have almost as many locations, so you don’t ever have to go out of your way to find one.
The only advantage 7-11s have is their Oden service. However, over the past decade (and also thanks to COVID) the number of locations in Japan that still offer Oden are rapidly declining in number.
