You want to make fried green tomatoes, but aren't sure if you should use unripe regular tomatoes or tomatoes that are actually green when they ripen (i.e. some heirloom varieties). The answer: use unripe tomatoes that feel firm and look full-grown. They have a tangy taste and firm texture that will stand up to frying; a ripe tomato would never survive the dredging and frying process.
Here's a basic recipe for fried green tomatoes: dredge thick tomatoes slices in flour, then dip in beaten egg or milk, and dredge in cornmeal; fry in 1/2 inch of vegetable oil, turning once until browned.
This is an excellent way to use those tomatoes that may not make it to fully ripe before the first freeze sets in!