Both Mila and Penelope are experiencing giant surges in popularity, so if that is your main concern, they might not be good choices.
Mila was not in the top 1,000 before 2006, but it is currently #174. It had a huge jump from 2010 (#364) to 2011 (#174), so it has upward momentum.
Penelope entered the top 1,000 in 2001 and is currently #169. That means that its rise has been a bit slower, with its 2010-2011 jump much smaller (from #200 to #169). But then there's the Kardashian baby, so Penelope might get a big boost from that.
In short, both of these names are trending strongly upward and look like contenders for the top 100 over the next 3 years. If that bothers you, you should look for alternatives. How about Mira (#787) or Calliope (not ranked)?