Just a different ester, like test enth vs test prop. Tren E takes longer to kick in but will yield higher blood levels once it does. I can personally handle 130mg/day or so of tren A, but tren E I can't go more than about 400mg/week before the pumps get too bad to lift. So I like tren A better, but really there's not much difference, just more or less frequent injections.