Just about everyone that sells diamond blades claim their blades are the best, and even if you are a diamond expert, it would still be hard to know good, better. best.
You can find them all over the net, Ebay being one source, and saw makers, etc.
You have to know what you are cutting to purchase the right blade. Look to the right of the last web site to see the various diamond blades and what material they are used for. You can easily get the wrong blade and pay dearly for your mistake, by short life on the blade.
I spent 40+ years working for a large general contractor. We used a number of brands over the years, but had EXTREMELY good results with "MK Diamond" brand blades. They are available through WW Grainger stores among other sources. Great performance, long lasting (compared to most others we tried) and reasonably priced relative to other brands.