I have tried a large range of watercolors and I always come back to Windsor & Newton. If you are looking to experiment and learn some techniques without spending a whole lot of money than The Cotman line of Windsor & Newton are going to be lower in price but be worth your time. Grumbacher also has a line of tubed watercolors that are acceptable, but their pan paints are terrible. Run as fast as you can away from Reeves or any comparable brand because they will: Dry chalky, always mix muddy, contain way to much polymer causing a booger-ey effect, fade in very little time, and because of the fact that they are very little pigment with a lot of fillers it is very difficult to achieve any kind of range of brightness causing you to loose depth and detail in your work.
As for Prang watercolor sets, I recomend those to anyone who is just beginning to use watercolors, they are very smooth and acheive a good amount of brightness. They will also behave enough like more professional quality paints for you to actually learn from them. I still use a set from time to time if I am traveling or need to make a quick sketch or touch up. Their drawbacks are the fact that there are limited colors and limited mixability, they also fade a little, and dry significantly more dull than when applied.
If your paints are grainy or chunky that may be because they have lost some of their moisture to solve this problem you can check out some watercolor mediums there may be one specifically for dissolving or reconstituting paint. Gum Arabic is one that tends to smooth things out. you can also apply some paint to your palet and then set it in the bathroom while your shower is running hot water, the steam will work wonders. The shower trick will also revive paint that has completely dried back to its original moistness so that you can continue working with the same palet.