I wouldn't suggest any dedicated graphics card for that APU given how weak the CPU is.
amd a8 6600k black edition base 3.6mhz and on trubo 4.2 mhz, 8 gb ram od 1600mhz
amd apu a8 6600k base speed 3.6mhz and on turbo 4.2 mhz quad core processor
Frankly those APU's just were never good for gaming, at least not when compared to a desktop cpu that didn't cost that much more.
As black zion already mentioned. That is a very weak APU. Any modern card would be severely bottle-necked by the cpu in many games. Not knowing exactly what you want out a new card. For instance do you want to play a particular game or have some other goal like smooth video playback?
Before spending any money you need to look at your task manager and look at cpu usage. If you are at 100% right now, no new video card is going to change that.
I will say that do to card availability, pricing and just flat out capability at the low end, in our current generation an Nvidia 1050ti would probably give you the over all best improvement, if any improvement can be had. They seem to be a bit less cpu dependent than the low end AMD cards are with weaker cpu's, but again the AMD cards low end cards might meet your needs too. We really don't know and can't say as you have not given us your goal.
As pricing is what it is right now on video cards. The best way to get a new card is with a new computer. Buying a card right now by itself can be double or more than what it should be. You might find with what you spend you could be half way to having just bought a whole new computer.
If you are in the USA and near a Micro Center and considering a new computer. Check out their Power Spec computers. Decent stuff, and I couldn't build it myself as cheap.