I faced the same dilema as you. My answer is the MKII is the best from YOUR list. If your MKI was in perfect condition that would make it more tough. But the op description sounds as if the MKI either has been shot a lot or previous owner could have taken better care of it. The mag release on bottom is a pain but my MKII puts them in the center everytime. They all are a pain to diassemble but its not needed to be done very often. You can clean em just fine while completely assembled. Good luck in your decision