You're approaching this from the wrong direction. Rather than pick the least efficient antenna for your situation, you need to focus on the most efficient antenna you can get. I understand - apartment, ground floor, foundation license. The deck is stacked against you right out of the chute. So then why use a 1% efficient antenna on top of it? As WX7G points out an efficient antenna that size could be 10% efficient. Not great but it puts you in the mobile antenna efficiency range which has a chance of working. At least shoot for that while exploring other options that could be even better.
Mark K5LXP
Albuquerque, NM