This is one of the most hottly contested issues on this forum, and it gets asked about 10 times a month. The long and short of it is, when you pick up a cue, if it feels too heavy for you, pick up a lighter cue until it feels right. People tend to spout about the advantages and the disadvantages of light vs. heavy, but it's all total hot air. It's purely a personal comfort thing which helps to build confidence. If you feel comfortable with a heavy cue, you'll play better with a heavier cue. Conversely if you prefer a lighter cue, you'll play better with a lighter cue. Most people prefer the weight of cue they learned to play with, and they feel they play poorly with something different.
Don't let all the silly debates worry you, your cue is perfect. If you're planning on buying a cue soon, go somewhere that you can test out many different cues. You can also try many different cues out in your local poolroom.
19 oz. is the most common weight because it's smack dab in the middle of the light and heavy end of the spectrum. Doesn't mean it's better or worse, it's just average.
If I haven't answered yor question, it's because there is no answer that suits every player.