What to use?

I either have winged root aphids or gnats. So tomorrow I'm hitting my garden supply store. My question is should I go with diatomaceous earth, mighty wash or something else? I'm looking to get rid of these and also prevent future problems. I read DE kills almost everything and is great for preventing bugs but is slow to work. I read mighty wash will kill also and fast. Any ideas? Again I greatly appreciate the help!

Also can you add diatomaceous earth to water and water your plants then let your pots get dry so the DE becomes effective again to kill these bastards