I have played both, and concur with Shahbahraz.
I DO feel that Aeronef is an easier start, and will have you itching to 'tweak' almost immediately. I found that a GOOD thing.
If you can find the add-ons David Manley suggested in some articles for Ragnarok, especially the 'altitude' variant, I know I wish I'd had given them a play.
I personally, to disdain of several playing partners, wanted to tweak IS as well. Can't give examples at the moment, as it's been a bit since we trotted out, but there were parts that just didn't feel right to me. It's complexity wasn't daunting, though.
I know: a bit vague, but the best I can offer.
Mind, even with vanilla rules, either have me saying 'you can't go wrong.'
Doug