A far as methods of murders go, strangulation takes a long time. Longer than it took Jodi Arias to kill Travis Alexander, and that wasn't quick, as Juan Martinez emphasized in court.
With strangulation, you have lots of opportunity to change you mind. Here's a quote from one case I found re: premeditation and strangulation.
Handler also testified that it appeared Sharp had struggled with her killer, that there was considerable force applied, and that the strangulation was prolonged.   When strangling pressure is applied, he said, a victim loses consciousness within seconds, and brain tissue starts to die within 6 minutes.   However, pressure must be continuous for at least 8 and possibly 12 minutes or longer after the victim loses consciousness for vital parts of the brain to die.  Sharp's injuries, he said, were consistent with the application of constant pressure to her neck for a period of 10 minutes
http://caselaw.findlaw.com/ks-supreme-court/1374172.html