As most of us know, there are at least two second seals available early in the game. In this topic I want to compile a list of the best uses for the early seals. Anyway, I'll start with some of the obvious ones and we can work our way from there.
The List
1. Robin to whatever you need. Robin can switch to any class so he/she can fill whatever niche your army needs.
2. Sully to Wyvern Rider. Wyvern Rider gives Sully some much needed strength. Also, discipline helps her get out of E axes quickly and her preexisting lance rank will carry over when she promotes to Wyvern Lord.
2. Panne to Wyvern Rider. Panne is another unit that isn't very good without a seal but amazing with one. Panne is easier to train than Donnel though.
3. Chrom to Cavalier.
4. Donnel to Mercenary/Fighter. Donnel isn't nessesarily the best user of the early seals but he has to have one to be usefull at all so if you plan to use him then give him a seal.