Well, I can give you THIS advice. I had the same issue a couple of weeks ago. Another member on here, WickedMojo, recommended the brand "Bayer." I went to Lowe's, and bought a bottle labeled "Vegetable and Garden Insect Spray." It cost $11, but was SOOOOO worth it.
Don't get me wrong, I would PREFER not to use ANY kind of chemical on my plants. BUT, keeping my plants healthy, and ALIVE, is VERY important to me. So, I sprayed them down with this stuff. IMMEDIATELY I could see dead aphids all over the soil underneath the plants. And knock on wood, I havent seen but MAYBE one or two aphids since then.
This stuff is friggin' AWESOME!
So, take that as it is. It worked WAY beyond my expectations. So, if you REALLY want to get rid of aphids, this stuff will help ya out. IF you go looking for it, they make several different varieties of the stuff. The bottle I got just hooks right up to the end of a hose. And ALL of the Bayer products are blue, fyi.
Good luck!
p.s. To my knowledge, I dont think aphids attack tomatoes. Boiling tomato leaves, and spraying the aphids with the juice from that, is a natural remedy for aphids.