Doodle is great for intersecting calendars with collaborators to come up with times for meetings.
However it doesn't provide a fast way to quickly mark time slots for "yes" or "no".
I've participated in Doodle poll that have over 100 slots for me check! Just imagine how tedious it is having to check off each one...
My new favorite is when2meet.com Excellent user interface! Super simple to use.