The caramel gene is a newer addition to the corn snake world and that makes it a bit more desirable to alot of people. There is alot to notice about it and lots of exciting things to mix it to. There are many unexplored traits for caramels that some selective breeding could enhance and really produce some new stunning looking animals.
But on the other hand the amel is well established and there are many attractive types that can already be purchased; reverse okeetee, florescent orange, sunglow, milk phase, candy cane, etc.
If you ask me what I prefer I would tell you amel. My first purchase was a pair of Motley Amel's (sunglow). I had looked at all the morphs I could see and found this to be the most attractive. I love their bright colors and nice pattern.
If you are going to have to choose between the two I would choose based on the beauty of the individual snake. I might normally be more attracted to the amel colors, but I would rather have a beautifully patterned Caramel than a busted Amel that isn't all the pretty. If you plan on breeding this snake ask yourself what you want to breed for. What are you trying to produce and what is more appropriate.
The guy selling you the snake is correct. You should pay more for an animal that carries an extra het. I would say that you could expec to pay around $10 more for this het. You should ask what the parents are and if you can see them that would be a good bonus. This should confirm presence of the het gene.
Good luck with your decision. I'm sure you will be happy with your new pet what ever you decide.
Aaron