In terms of performance the i5-3210m is better because of the higher clockspeeds. Haswell CPUs are on average about 6% more powerful than Ivy Bridge CPUs, but the "u" means ULV (ultra low voltage) CPU which consumes less power mostly at the cost of some performance.
The link below from Intel's site compares the two side by side.
http://www.hardwarepal.com/battlefield-4-benchmark-mp-cpu-gpu-w7-vs-w8-1/4/
The integrated Intel HD 4600 is around 30% more powerful than the older Intel HD 4000. If the laptop has a dedicated graphics chip, then it does not make too much of a difference.