Chris,
A "packer" is the whole brisket which includes the point and the flat. There are two advantages to getting a packer. 1. The price is much cheaper 2. You get to trim it the way you want it. Typically "flats" are overly trimmed of their fat which is a bad thing when you are cooking low and slow. So I'd suggest buying a packer and either separating the point from the flat prior to cooking or after. I separate prior and chop the point and slice the flat when they're done. If you can't find a packer, look for a flat with a good fat cap. I'll find the link that will walk you through the separation process.