As much truth as there is to "let the fish tell you," it doesn't really make sense as an answer when someone is asking a question like this. I think what most users want is some pointers or personal experience, in other words, what has worked personally for YOU in the past. When the bite is tough but I know fish should be feeding on topwaters, I will throw a small popper. Also, I like throwing poppers when there are a lot of emerging forms of cover that come up out of the water. For instance, I will throw a popper, work it for three or four pops, and pause it next to wood, or lilly pad openings. This works extremely well when fish are holding on cover. I also really like throwing poppers when fish are in somewhat of a lethargic mode. I like throwing buzz baits mostly during spring or when I know bass are on the move and feeding heavily. Do not be afraid to work it fast, fast, fast. Also, don't be afraid to work it slow either. I would say that here in NC where I live, the next month or maybe even two will be GOLDEN for buzz bait fishing. I also like to throw buzz baits where there is a lot of emerging forms of cover. I also find that it works extremely well when throwing into shallow flats. You can really cover a lot of water and fish can see the bait really good in these situations.
When fishing a lot of leafy cover and vegetation, I will throw a frog of some type. If I would have otherwise wanted to throw a buzz bait but the vegetation is too thick, I will throw a horny toad. If I am around lilly pads, want to fish more of a popper style bait or I am looking for a bigger bite, I will throw something like a spro frog. Spooks and other walk the dog type baits have worked best for me when the fish are really keying in on shad. I have actually had more success with this bait, personally, when the water is a little bit clearer. From my experience, this is a really good all around bait and works wonders on open water. It is a really good search bait.
You should definitely experiment. The fish in the particular body of water may also just prefer one bait over the other. As others have said, "let the fish tell you." However, the above I believe are pretty good general ideas of what you can look for---they have certainly worked well for me.
---Carlos