Not once have I heard about Mapwriter being laggy; I have heard numerous times about Voxelmap being laggy.
Edit: If you really are having lag problems, I recommend setting the priority of Minecraft or javaw higher. I did this last night before I went to sleep and tested it, and I think I was getting 60+ fps. On Windows you can do this through the task manager, and on OSX you can do this by running sudo renice -15 PID. Replace PID with the Process ID of Minecraft or javaw, you can find this in Activity Monitor. -20 is the highest priority possible, so you might want to set it to that depending on the amount of lag.
You could also turn the size of the minimap down, and disable it when not using it (not from the pack, just turn it's visibility off). Same goes for NEI. Personally, I don't like playing with NEI open, not because of lag (well kind of because of lag), but because I like seeing what's going on around me, and seeing all the items on the side distracts me.