My preference, from best to worst:
#3 Great Trader (Because it has the 'Great' in its name to avoid confusion)
#4 Trade Caravan (While I like this better, the lack of Great means that it might be confusing)
#2 Great Peddler (Sounds better to me then Merchant, which sounds anachronistic to me)
#1 Great Merchant (Familiar to all, and has Great in it)
#5 Merchant Caravan (not Great, and still merchant. Still, I rate it higher then Great Merchant if it wasn't for the convention of having great people start with Great).