Depends a lot on your playstyle - Corrin is much tankier physically, and cordelia is a glass cannon - maybe too much with those IVs. On the other side, Triangle adept is very much a blessing under the current meta.
The safer bet is probably to promote Corrin - At 37 Spd and 34 Def she can work quite well as a damage dealer and as a tank. But again, depends on what you want either for. Also, Ninian has Ward Dragons, which can be interesting with Corrin. But you'll need something to deal with high Res characters.