There are only 2 real differences between the systems.
1)The Acer has DDR3 memory vs the DDR2 in the Lenovo. In reality, unless there is a large difference in the speed of the memory, there isn't going to be much of a difference.
2) The Lenovo has a larger HDD. This only matters if you need a lot of storage space.
I personally like the build quality of Lenovo's over Acer, so the Lenovo would get my vote.