Intel's proc in Zenfone 2 is a little bit more powerful from the cpu side but slightly weaker on the GPU side, they are about equal in general.
Zenfone is like any other Intel's smartphones a lot cheaper for their performance class compared to Qualcomm's.
Android is not really optimized for Intel's processors, thus you will see more hick-ups and some compatibility issues.
1+1 does not have MicroSD slot, Zenfone 2 yes.
1+1 has more internal memory.
Zenfone 2 is cheaper than 1+1 but has some downsides due to Intel's proc.
1+1 is a lot more superior in term of ROM support (CyanogenMod) and you can find plenty of custom ROMs, more than for Zenfone 2.
ASUS has better customer support than 1+1.... a lot better! trust me!
1+1 does not support several specific LTE bands.
Zenfone 2 has more RAM...but I do not think is a big different
You can simply go to local stores to get Zenfone 2 but for 1+1 is not the case.
Info: I own and use 1+1 for daily basis since July 2014.
I would go for Asus zenfone 2 because of its hardware. It's atom cpu perfoms better than the snapdragon 801 and it also has 1 gigabyte of RAM more. Which is nice if you're into mobile gaming.
Other things like picture quality are pretty much the same.
edit: I looked up the benchmarks again and the cpu's equal eachoter in performance.
Zenfone 2 (or even 5) for all the reason mentionned here, plus (humour) they all come with
Dual SIM card slot FACTORY UNLOCKED means out of the box, slap in 2 sim cards + SD card
You get 2 phone number of the greatest phone
Have one my self (Asus updates apps VERY frequently, sometimes OS)