More info is necessary.
Assuming the same clockspeed, Haswell is on average 6% more powerful. Unless you run benchmarks or you do very CPU intensive tasks that takes a long time, then you will not notice a difference. For example, if you encode videos an it takes Ivy Bridge 360 minutes to complete the encode, Haswell can generally do it in about 340 minutes.
Haswell CPUs generally consumes a little less power so battery life will be longer. An extreme example would be Lenovo's claim of a 70% improvement in battery life for the 2014 ThinkPad X1 Carbon. However, I am sure such a large improvement is due to more than just the change in CPU.
If you are relying on integrated graphics to play games, then you will want a Haswell generation Core i5 CPU with the Intel HD 4600 graphics core which has approximately 33% better performance on average than the Intel HD 4000 graphics core in Ivy Bridge.