[Sevens]

I have a -LOT- of powders but some I don't use much, or don't use much anymore.

I like a powder that meters well.
Spherical powders and extremely small flake powders do great through my Lyman 55. Power Pistol, anything by Accurate, Titegroup, 2400, Longshot, etc. These all work well. Blue Dot, Green Dot, Unique and IMR-800X are at the far other end of the spectrum. This isn't as big a deal with heavier charge weights, but in small charges, you get erratic drops and erratic performance.

I like a powder that has good published load data available.
Hodgdon's online Reloading Data Source is an extremely quick, flexible, powerful and enjoyable to use resource and it makes me ALWAYS look at Hodgdon branded powders first. At the other end of the spectrum, Alliant's online data source is extremely pathetic and what's worse is that they've copied the result of the website for their published guide. I typically refer to my 2005 printed Alliant guide because it was the last one they made before they went stupid.

Obviously, there are many other published sources and I have 3 popular large manuals and you can sometimes get good load data from the bullet manufacturers, too, but I like to get data from the powder distributors.

I like a powder that is widely available and not overly expensive.
That means I've avoided Vihtavuori powders for more than 20 years. From all I've read, they are FANTASTIC powders in many different ways, but I can accomplish what I set out to do with powders from the more common powders, so I've stuck to them. I've also not bought any Ramshot powders for the same reasons though I'm sure they are decent as well.

I like a powder that returns a high velocity and a full charge that takes most of the available space.
This is merely an indicator that you are picking a powder of the proper speed & type for the use. Using ultra-fast burning target powders in hardcore, high-pressure loads is a HORRIBLE idea and I don't support it no matter what drives someone to do it. Using the proper powder gives better results -- and YES, it forces to buy more powders and it limits how many different things you can do with your ONE powder but it pays off in performance and safety. You won't see me building .357 and .44 Magnum loads with Bullseye and Titegroup even when my load calls for three times as much 2400 than you can get with W231.

A good way to choose a powder can be to make your own criteria (or borrow someone else's, if you like their argument) and then start a thread asking for suggestions.

Don't say, "I want to load .357, what powder should I get?"

Instead say, "I want to load .357 Magnum for a 4-inch S&W 686 using 158 grain jacketed bullets. I'd like to make some midrange loads that my 12-year old can shoot and I'd like to try some real barn-burners that push the limits of the caliber as well."

We know that you can shoot 148 grain swaged hollow-base wadcutters in .38 Special at 750 FPS and you can shoot a 180 grain JSP at 1,200 FPS through the same revolver but don't expect to be able to build those loads to the best of their abilities with the same powder.