I have used the Lifepak 10, 11, 12 in pre hospital settings. All were good. I am partial to Philips MRX but only because we have been using them for a while now. 12 leads seem easier than LP-12, transmitting also easier but again, preference. I dd have the chance to use the Zoll X series and loved it. The drop it weight, 12 leads, transmitting / blue tooth is easier than MRX. The drop in weight is nice, especially, if you have to hump the fucker on a 4 floor walk up for a code, or 14 times in a 24 hour tour.
M.