Nickel-penny composition for voltaic cell

BuddyPal

I was organizing pennies into categories based on what they were composed of; before 1982 (I believe) pennies were made out of 95% Cu, and after they were made primarily out of zinc. I thought that the ideal penny for a voltaic cell would use a Copper penny, and a Nickel. However, I found that the composition of Nickels is 55% Cu. I care a lot more for this specific project because my physics class has turned it into a competition for highest voltage. I would test these metals myself but I do not own a voltmeter. =(

Specifically my question is; should I use 95% Copper pennies along with 55% Copper Nickels, or should I use 97.5% Zinc pennies along with 55% Copper Nickels for the highest voltage? Or better yet, are there other cheap and easily found metals that work better than these?

P.S. What kind of liquid (preferably non-odorous) should I use as an electrolyte?

P.S.S. My impression is to use zinc pennies and copper nickels, mostly because they are the most different, if this is the case, should I strip the covering off of the Zinc pennies? -unless that's illegal of course-