I am not surprised that you got little results with your 25% peel. Unless you do many of them, this is often the case. A 35% peel may indeed give you the results you want, depending strongly on how it is applied.
In general, the deeper the peel, the stronger the results are. However, the risks—including risk of hyperpigmentation (to much pigment) or hypopigmentation (skin whitening)—also increase along with it. Also, the recovery period is longer with a stronger peel.
Nonetheless, with a stronger peel, the top layers of the skin are destroyed (hence the darkening and then peeling off of the skin) more effectively. When the top layers are destroyed, the body is forced to regrow or regenerate fresh new upper layers of skin, collagen and elastin that give the skin a younger, smoother, less-wrinkled, and more even-pigmented appearance. Given the fact that you have told me that you have light skin (post-peel pigment problems are less common with light skin), I would agree that you consider a stronger peel to get the results you want.