great question
I think saying "uh" (or that upside down e sound) is most always going to sound "normal" to American English speakers. But we do use the long a (you spelled it ey) to give a very slightly different meaning.
If I say "I ate "uh" sandwich for lunch", I mean my lunch was a sandwich and not something else for example. If I say "I ate "ey" sandwich for lunch", I mean that today I only had ONE sandwich. (and maybe on other days I have more than one or maybe I wish I had more than one or something of that sort. )
I also think that some people use "ey" more often in more formal settings (I suspect this is a class thing) while other people would think it sounds stiff and awkward. I would have to pay attention to it for a while to figure out the subtle rules of it. I think I am maybe more likely to use "ey" (again, only in formal settings) in front of certain words than others. It may depend on the sound for the word following or it may just be idiomatic.
My suggestion though is to stick with "uh" unless you mean "one".
Of course remember to use "an" in front of words that start with a vowel sound.
![Wink [;)]](/emoticons/emotion-5.gif)
Aint English awful!