In general, you may find a constant air pump gun to be a good initial investment. The gun will not break your wallet, and it will not cost too much to feed. As you learn to play, you will find that you can hold your own against many semi-automatic guns out there. A pump's slower rate of fire may encourage you to learn better basic personal tactics as well. Fortunately for the paint manufactures, and unfortunately for you, that's something you have to find out yourself.
Different guns tend to like different paint.
Other factors such as the weather, how fresh the paint is, etc., can all effect how well your paint performs for you. There are a few brands which are well known for their high quality, however they still may not perform in your gun as well as a less popular paint. The only sure way to find out what the best kind of paint to use is, is to try several brands through your gun. The 1993 year-end edition of PCRI contained an article testing most brands of paint on the market. On the contrary, most players do not use ZAP, finding that RP Scherer shoots better in most guns.