Yeah, Circle Y makes great saddles, but those two are different sizes. Do you know what size you need? They are also different weights and trees. Make sure it will fit you and your horse before you buy.
If you horse is high-withered do not get flex tree (it's not the cheapest one either, frankly). It may sit right on the withers, which is not good.
First saddle is very nice price for the new, which makes it little suspicious (also the seller has only 9 feedbacks).
Personally I found that 15 and 16 sizes DO feel different, but it's a matter of taste... :)