BN plecos are pretty good algae eaters, and they will stay small enough for your tank. You might wanna check your water parameters though to make sure you don't have an excess of nutrients feeding the algae growth.
Sailfins and "common" plecos get too big for a tank that size, plus they eventually will need to have their diet heavily supplemented with foods besides algae, and they may stop grazing on the algae together, so you'll just end up with extra bioload and another mouth to feed.
Snails are good algae eaters if you get the correct species, but some of them won't make much of a dent.