SSD + Optibay HDD is my vote 😀 (I know it'll set you back $200 though...)
Once you use an SSD, you'll won't be able to use a standard HDD again (but it's good to have it as a 2nd storage drive). You can pick up an external DVD burner for ~$20...that way you have the best of all worlds - SSD speed, HDD storage, and ODD when you need it.