Good question....I actually had to go check out my copies to determine what it was you were after.
Most of my Redwall books are the "Mass-Market" edition from Ace, which is essentially the "second edition" of the books because the first was through Penguin. It says this right on the inside of the cover...Penguin's copies went out a year earlier than Ace's. My copy of Redwall is the first edition from Avon, printed in 1990; the cover is very different from those from Ace. I was a tad bummed I didn't get the Ace cover because then all my Redwall books would look somewhat alike.