AVO and AMEC make the best meggers IMO. What is most important is what voltages you will need and what features. For LV system basic testing I like the old hand crank style. I like to be able to "feel" the resistance, or maybe I am just old school.
For larger jobs I like my AMEC that stores the data that I can print out later, it also does DAR and PI automatically for me, great time saver for big testing jobs.