Generally speaking, I think that the founders of a startup company are probably better off with a convertible note financing over a Series A financing in a seed round for a couple of reasons.
1. A convertible note avoids setting a valuation for the company. In a seed Series A, the valuation is probably going to be fairly low and difficult to determine. Even if the convertible note converts into the eventual VC Series A at a discount (or also has warrant coverage), the amount of dilution suffered by the founder in the convertible note is less than the dilution suffered by setting the valuation low in the seed Series A. This assumes that the valuation at the time of the seed financing will increase at a rate greater than the discount/warrant coverage on the convertible note. People good at excel should try to model the different scenarios.