How to choose not only juicy lemons but lemons with less acrid flavor

For skin thickness: thick-skinned lemons have a specific appearance. They are larger, their pores are frequently larger, and their skin is somewhat lumpy. Pay attention to these criteria before and after you cut a lemon, and you will soon learn to recognize the difference between the very thick skinned lemons and the thin skinned ones.

As for the bitterness, I don't think there is a trick (or if there is, I don't know it). Make sure you are always using freshly squeezed juice, because either storing the squeezed juice or, to some extent, squeezing juice from a lemon that has been stored cut, makes the juice turn bitter. Also, the skin and the cell walls are bitter by themselves, so make sure you are squeezing properly, without getting too much pulp into the juice. But these are variations in bitterness related to the use of the lemon - as for the variations due to the lemon's grown amount of bitter compounds, I don't think you can know it beforehand.

For thin-skinned, you can try pressing the lemon, they are thin-skinned if you can kinda feel the lemon flesh. While if it is thick-skinned it will be very hard to press. (i mean press in a way not to destroy the lemon).

Generally, the deeper the yellow color, the less sour the lemon is, as it is riper. So if there is any pale yellow or green, then it is not ripe enough. All citrus fruits are green while they are still growing on the tree. As lemons ripe, they lose their green color because the chlorophyll pigment is replaced with a chemical called anthocyanin.