Choices 'could' be endless as long as your willing to set the tank up pending the plec species requirements.
You originally was going for a rather larger plec (the royal) so is your choice limited to larger species? or doesn't it really matter?.
Whats the temp of the tank, what decor (ie wood, if any) is in the tank?, Whats the filtration on the tank?. If you decide on a larger species plec then obviously the bio-load and mess is going to be considerably higher than some of the much smaller species.
Some of the above species mentioned are relatively nice and possibly good choices 'but' require different things in the way of tank and dietary requirements, so unless we know what the conditions your planning on or currently have we couldn't tell you here or there on a species which would ideally be suited.
Out of the species mentioned above the choice for me would be the L128, stunning plec which grows to be a nice larger species which may well be better suited to your tank than some of the smaller species mentioned. The other option to the L128 is the L200 green phantom, equally as stunning. Both can be found for the average of £35-£55 if you shop around.
