Delta 100 is a newer technology film making it, IMO, smoother and sharper than FP4+. FP4+ will give you a more traditional look. A sort of comparison would be between Plus-X and TMax 100. I have a personal love of Delta 100, but we all have slightly different tastes and either will make a ridiculously good 11x14.
You can't go wrong with only a 25 sheet box and you will enjoy either and eventually both.