I can't belive you did or are even thinking aboit trading a ST for a pleco.
In the end it is up to you.
Lets compare them for a second though...
ST- a very beautiful, personable fish. It will come to the front of the tank and greet you, beg for food when you walk into the room. They are aggressive feeders. They get MORE impresive with size. They are getting more rare by the day.
Pleco-They eat veggies and algae waffers... they will more or less will only move a few inches at a time, it at all. They will never come to greet you when you walk into the room, instead they will flee and hide! They will lay on the bottom of your tank looking like what they are CRAP!
I will warn you now. That pleco will scratch the crap out of you acrylic tank!