I love the pods. Have never had problems with them not dissolving, but I haven't been using them for long yet.
Gave up on powder years ago as it always left white specks on the washing, or, worse still, you could see the pattern of the holes in the drum on dark fabrics. So I've used liquids for years now. This was as a result of reading an article in the "Test" (The German version of "Which") which recommended using liquids over powders for that very reason.
In the latest version of the same test, they revert to recommending powders but after my previous experience I'm sticking with the liquids, and am now changing to pods because they come in plastic bags instead of those bulky bottles and make for less waste. I like the feel of them, too!! (Odd, or what?)