hamburgman is right on most accounts.
Pour-ons are the least effective - sure, it's easy to squirt it on 'em, but hellfire, if the majority of the drug doesn't get to 'em to kill 'em, why use it? Never used 'em, never will.
'Rotating' dewormers has been misrepresented and misunderstood - and too many veterinarians do it wrong and make inappropriate recommendations to their clients. Proper 'rotation' does not mean "Use something different every time you deworm." - doing that really does speed you down the road to selection of a population of parasites that's resistant to everything.
Rather, you should pick ONE product, and use it until it no longer works on the parasites on your place (hopefully 2 years or longer), then switch to another dewormer in another class and use it 'til it no longer is effective, then switch to another class of dewormer
Take some time and watch this video; might open some eyes.
Dr. Tom Yazwinski - Internal Parasite Control in Beef Cattle on Vimeo