android has no >KNOWN< exploits since 3.0, prob earlier. That's how 'noob mode' jailbreakers work. ios def has android beat as you always have to be careful with updates (vs bootloader-unlocked devices, some of us completely refuse to buy locked-only devices)
they both likely have more, but if you dont know about it it might as well not exist.
Unlocked devices like the S5 you only need to learn once and to re-root takes 5 minutes including reboots. You never have to worry about not being able to root on it and the like.
I'd imagine more android exploits will be found as ICS is available for bootloader-locked phones, HC more or less sidestepped this issue.