I would stay away from anything that introduces water to the ear canal. It can end up promoting infection with a small amount of standing water and creates an environment that can exacerbate the issue. Same goes for Hydrogen Peroxide as its H2O2 and once it bubbles up you are left with H2O.
What we have used on our girl that occasionally had some ear issues is white vinegar on slightly dampened cotton balls. It works great, and won't promote infection. We also have some ear wash that the vet recommended but I was unable to find it, and we have only used it when her ears are really gunked up.
Also, I don't like using cotton swabs unless you are really confident about how well you can control your cat. For our girl Pixie, it's pretty easy but I wouldn't think of using them on the other 3. Just too big of a risk with a cat that wants to squirm and isn't wild about the idea in the first place. With Pixie, she knows she's going to feel better at the end, so she's pretty tolerant.
On a personal note, I spend a fair amount of time in the water and have had ear issues for a long while. I have got in the routine that when I go swimming I use a 50/50 alcohol vinegar solution to rinse out my ears. It displaces any water, the alcohol evaporates and the vinegar takes care of anything that would promote infection. The alcohol definitely isn't something a cat would tolerate, but has kept any ear issues at bay for me for the last 25 years.
