There are scoring charts in the download section of this site that could give you a good idea of which event is better for you. In addition to the charts however consider your local and / or state competition level in both events as you may be able to take advantage if one of the events is particularly week in your area.
Do these scoring charts also apply to younger kids, ie ages 10-13. Here's my question. My 10 yearold daughter just ran a 1:08.15 400 at the school league track meet Saturday, which scores 659 on the women's scoring table. She's never been competitively timed in the 800 and I'm trying to ballpark what she's capable of. Does this mean that if her 800 abilitiy (and level of conditioning) is comparable to the 400, that she would be roughly projected to do a 2:31.74 in the 800 (also 659 on the scoring table). My instinct tells that she is a better middle distance runner than sprinter, although she is good at both.