I'd look for trips requiring connections to places where DL competes with a LCC. BWI or MDW could work. Or look at places where DL wants especially to compete with AA/US or UA/CO: their hubs or focus cities like BNA, STL, RDU, AUS if you don't want to just search randomly.

Alternatively, where would you enjoy spending a weekend? Perhaps AUS, BNA, or MSY would be fun. NYC is likely to be expensive.