I started out with quarters, switched to halves, then dollars. It's all about what you're accustomed to, as halves feel pretty small now. Quarters? Feel like pennies now. I say halves and dollars are the way to go. Who cares if the coin you're using is unusual? Make up a story and you're good to go. Quarters can go out of circulation for all I care.

Just kidding, although I never use quarters...
If someone walked up up to you and wanted to show you a card trick, and brought out this really weird looking deck of cards, that he claimed to be normal. He asked you to inspect it and you did, yet he pulled off some really big shot magic trick. This doesn't fully work on you since you're a magician, but it's the ideal. Both you, and a layman, even though inspection will consciously (if not, then subconsciously) still think there was something sneaky with that deck of cards. When you show them something completely impossible and illogical, they will naturally search an explanation, when none is to find, it's always that weird deck that sticks out of the mass. If it's gaffed or not is not of the point, as long as it is something completely new and devious, they will never fully trust it.
Theatrehead, in my opinion small hands are a blessing. You can make common coins (small in other hands) look relatively big in yours. And also, small hands covers less (you will still be able to palm as good, they just wont think you're as capable of it), which earns a lot of trust in the spectators mind. Remember, those who got nothing to hide, hide nothing.
Since all the coins you have showed there seem to be common currency you should stick to what seem to be the best. Take some things into mind:
Which coins are you very likely to encounter? (a borrowed coin does not only make the spectator feel important and extra interested, but also gives a lot of trust)
Which coins looks the best after a vanish or spellbound change? (regarding its size, shape, color... bigger sizes makes vanishes more visual, shinier coins also makes vanishes more visual)
Which coins can people mostly relate to? (if there's small currency people usually got, but hardly ever use, the value and participation from their side lowers, thus the interest span becomes shorter and it makes your life slightly harder)
Also remember that, if you're not comfortable with something, work with it until you are(this statement is to be taken with reason, if it cuts your hands or just doesn't work for you, it's obviously a bad choice). I don't think anyone here felt like they were playing home base when they first tried to get into classic palm.
Good luck mate!