My opinion doesnt count because its obviously biased.
Go to the store and try them both! I've tried them both and I know which one I would go for!
Personal opinion:
- Quick/easy fold - IF win (No question)
- Roll when folded - IF win (While having extra little wheels on a rack is great for smooth surfaces getting in and out of trains and down stairs is not very useful, this is IMO where the iF wins hans down, the magnet that holds the wheels together is very strong and you can easily bounce the bike from step to step, this is a must have for me in the london underground.)
- Compactness - Brompton win (No question)
- Comfortable ride/steer Personal choice
- Light weight about the same
- Has at least 3 gears - Component wise, Sram with brake disk make the iF win
Best of luck!
Juan