Bristlenose plecosare suggest for planted tanks as they tend to leave plants alone and eat algae very efficiently.
I would suggest a shoal (6 or more) Otocinclus, also known as Dwarf Sucker Catfish. They can keep a tank pretty clean of algae, and won't hurt your plants. I keep 3 in my 55 (i would get more but the tank is already overstocked) and they do a bang-up job. They are housed with firemouths and are left alone. I would just give them plenty of places to take refuge just in case your FM's take an unwanted interest in them.
I would second otto's they are fairly quick to get away from SA's. I currently keep Siamese algae eaters in my 30g w/ 1FM and 2JD the fm and jd are fairly small though and i havent even a tail nip on the sae's
I'd just go with a bristlenose or two - they're tough, firemouths will generally ignore them, and they do a better job of algae control then otto's - they're also a lot less sensitive to poor water conditions if problems arise.
I would say it depends on your plant species ... I've had bristlenose that demolished various stem plants but leaves anubias, swords, crypts and ferns. If I had a lot delicate stem plants, I'd go the otos ...