Arlo ranked 189th in the last stats and was still rising in popularity. The suggestion is it has a while to go before it does. A lot of the baby naming websites are tipping -O sounding names to be the next big thing in trends. Think Mylo, Juno, Harlow, Arlo, Willow, Marlow, Margo(t), Monroe, Indigo, Shiloh, Hugo, Rocco, Orlando, Romeo, Leo. All without exception on the rise.
Adam is currently gently on the decline, though still popular ranking 40th.
Oscar ranked 7th and has been rising for a while and the last stats gave no indication that we've yet hit Peak Oscar.
So I think you have a difficult choice if you want popular but not too popular. Both Arlo and Adam might be a gamble. Personally I think you should steer clear of Oscar if popularity is a concern to you.
Arlo is probably more prone to fashion trends and could date badly but is different. I think Arlo is currently in very middle class ground, but if the trend really takes off, could be one that doesn't stay there. There have been a few celebrities who have followed it, which could have an impact.
Adam is more classic but could be classed as 'dull' or 'safe' depending on your view point. Its unlikely to ever go completely out of fashion or have quite the same level of class associations and potential problems.
The real question is more about how much YOU like it though and whether indeed you are picking it to be deliberately different - like a lot of other people.
My simple answer is really, if you like it, go for it and stop worrying about everything and everyone else.