Champ. Up until him, I had immersed myself in upland hunting training (primarily +P and -R) and CM crap, mixed with some crude/unstudied rewards. I didn't have the stomach for a lot of the more intense methods, but yeah, I did more than enough that I feel guilty about now. Fortunately, we had sense enough to treat puppies totally differently, so we didn't screw up the litters we'd raised.
It was clear our approach to adult dogs was not going to work for Champ as he matured, and I very skeptically decided to try marker training, which I had originally read about on Leerburg's site--figured since this old school trainer had given this 'silly pet method' a try, what could it hurt. When I saw how effective and fun it was, I was pretty happy to leave the old stuff behind and continue to educate myself.
Honestly, I have no intention of ever going to a "balanced approach." Yes, I recognize that all four quadrants are effective at changing behavior, but I don't think using all four is automatically warranted, especially when focusing on PR can achieve so much. I really like the Humane Hierarchy principle. Another guideline is LIMA--least invasive, minimally aversive, although I feel like that gives a less comprehensive roadmap. Both of these hold the trainer accountable to be creative and critical thinkers.
Anyways, the most difficult thing for me has been patience. I'm not blaming the actual training methods I used to use for struggling with this because I realize that all trainers, despite values and methods, should always be acting patiently and with clear thinking. However, resisting making that verbal correction or doing that leash tug is hard, when so easily available, is hard and takes self-discipline for sure!
Another thing is holding myself accountable (and trusting the system) when I am the only one in my family trying to focus on PR. Normally, this isn't an issue because I live alone, but when I go visit, it becomes a notable point of contention. I did actually go to an e-collar to train Elsie to stay on my parents' property, which was no big deal to anyone but me--I could explain the reasons if anyone is interested--but what I want to emphasize is this: I felt like I was cheating and hypocritical (I was), I felt lousy (as I'm sure Elsie did), I do wish I'd have tried the methods I recommend now (I was aware of these of course with Elsie, but I didn't have enough faith given her history), I did absolutely, despite using it as judiciously and correctly as I could, have fallout, and without a physical barrier (ie their hydro gates open), all bets are still off <--so I should take this opp to train her with pr again. My point is, it's easy to revert for those things you have built up in your head to actually "needing" it, and I'd encourage you to step back when you hit those walls, and consider other options (or ask here).
One of the things that drives me to 'stay positive' with all my dogs now (with Champ especially, since he is the only one with minimal experience with my old methods) is that I want to love them now and look back at them later 100% because of the amazing dogs they are/were, not poisoned by 'love mixed with guilt.' I will never be perfect and will always think about things I could have done/handled better, but it keeps me trying. A less selfish drive, of course, is the fact that I'd love for them to live without fear, discomfort, and pain as much as possible.