I don't think it's a good idea to work on more than one project, but that's just me.
I usually take a look and decide what would be the most interesting for me to work on at the time. I figure if I am interested, I'll stay motivated and therefore have a better chance of completion.
If money is enough to drive you, try to find out which is more profitable should do it, but being useful and good to people and mankind in general is an added bonus and motivation.
Do you want to realize the ideas for fun, for profit or to learn something?
Ask them which one you think is best/most likely to be a product they would use. Tell them it's okay to say none of them. If no one thinks those 3 are good move on to the next.