Like anything in EMS and medicine, you will get a variety of opinions. I have yet to find a design of an oropharyngeal airway (OPA) that didn't work. Some like the Berman-style OPAs (those that are built like an I-Beam) because they are easy to suction around... and there is some validity to that but I have yet to have an issue suctioning around an OPA. Some like the color-coded OPAs (Rusch or Guedel) you mentioned because of the color code... which in my experience only makes restocking easier after a call.

My preferred OPAs are made by Hudson. These are the common transparent green airways that are semi-flexible. I prefer these because they seem to not clog as easily as the Guedel airways, are not as rigid and they hold up in the heat much better.

Both the Guedels and Berman airways are susceptible to deformation while stored in the heat. The Guedels/Rusch airways are especially effected by heat, with the flanges cracking and rolling when stored for any period of time in over 100deg heat. The Hudson OPAs do get softer when hot, but even here in Hades The Valley of the Sun they still work just fine.

In the end, all work, and any one is better then not having any. Before carrying OPAs I would get the proper training and of course, make sure it is within your scope of care where you live and work.

OPAs are good, but if you are allowed and you need to choose between the two due to weight/space considerations, consider only carrying Nasopharyngeal airways (NPA). If space/weight isn't an issue... carry both.