Might be better off putting a post in the plec section of the forum... but:
There is a few more things we need to know...
*Tank settup
*Tank temperature (not just coldwater/tropical)
*Tank Mates (or idea of...)
*Substrate (gravel or sand?)
*Job (do you need it to eat algae?)
Do you have something in mind?
Not all (in fact not many!!) of the L (loricarridae) plecs eat algae, so when choosing, you are best researching species first, like you are, dont buy on a whim!
There arew the Bristlenose Ancistrus (there are actually many species under this name) but they are the best algae eaters! Can hit about 15cm (i have a 17 year old male who hit 19cm but he is a monster and outliving everyone!), LDA 25 Pitbull Plecs, great algae eaters but get to about 7cm so maybe havea few?...
Or are you looking at more fancy plecs like Golden Nuggets or Chocolate Zebra Plecs? They would be happier eating a mix of algae and prawn/cockle/muscle etc... not great algae eaters...
Or the giants like the common plecs sailfins.. (gibbiceps) etc... TBH i dont even condone housing these guys to 8ft+ tanks.. they just need so much more space than that!!!! I will help people who already have got them but NEVER advise buying them... these fish get so big.... if your tank is 4-5ft front to back and 3 times that in length and height then maybe....
There are far easier plecs out there to get hold of...
Or there are the other more fancy 'monsters' like the Panaque (believe me... when you have a 25cm+ panague decimating your tank and mincing very expensive ornaments and wood...) and Glaxy Plecs (another big monster).
Most 'fancy' L-Number Plecs get from between 15cm to 30cm... but most need a good dealof protein in diet...
Candy Stripe Plecs are the only one i find to be fancy and good algae eaters.....
Any more ideas?