When choosing a sinker you want to think about two things. How far do I want to cast? And, How heavy does my sinker need to be to hold bottom?
In most lakes and ponds where the water does not move, you can use a sinker of any size. The sinker size you are using in ponds usually depends on how far you want to cast. In general, most of the time I am using a homemade one ounce no roll sinker. That seems to cover all bases in pond fishing. It can cast far or in close, fits in well with many outfits and method packs well around a sinker this size.
Moving water is a completely different story. I have sinkers I use from 1-4 ounces when fishing river currents. It has to hold the bottom and sometimes a large sinker is needed to do that. Realize that large sinkers can also put a strain on your equipment. When fishing river currents with a three ounce homemade in-line lead, I am generally using my big twelve foot rod that can handle the weight of the sinker along with a couple of ounces of method mix packed around it.
I make all my own sinkers these days with molds I bought from the UK and here in the US. The two kinds I make are no roll sinkers in a mold produced by the Do-it Company and a three ounce in-line lead from a mold from a company in the UK. I like to paint my sinkers (using powder paint) to blend in with the bottom, a sort of camouflage. Most serious carp fishermen in the UK use camouflaged sinkers, and I do think it give me a slight edge. I usually paint mine either a weedy green or a sandy brown (see photo at right).