When you're on the lookout for heirloom tomatoes you should look for a few things! 1: they need to be slightly firm. You dont want anything too soft. 2: you also want them to be fragrant, aka they need to smell LIKE A TOMATO. If they don't smell, skip them! And lastly, 3: don't be afraid to go for the weirder colors like the reddish brown or green tomatoes - they are delish!