EasyWorship uses whatever resolution and aspect ratio the computer itself supports and uses. I would try to talk him out of going 16 x 10 though as it isn't that common and you'll find it a lot more difficult to find backgrounds and other media (especially video) in that aspect ratio. Videos will still play at their native aspect ratio with black bars at the top and bottom unless they are stretched (which looks terrible) making it difficult to use them as backgrounds. Visiting speakers, music groups, etc. will only have 16x9 media to display as will any purchased or provided media from outside sources.
The few times you would find it useful probably won't justify the additional cost, limitations, and aggravation of going 16x10 instead of 16x9.