Either works. Both are good as a supplemental food once or twice a week. Most tortoises don't like the LS version at first and it takes some introduction to get them to eat it, but its worth the time and effort.
Most Mazuri that you are likely to find will be the newer LS.
The "regular" type 5M21 is increasingly hard to find. And even then, mostly sold in the large 25 pound bags.