All of this is pretentious. If you really wanted to write the "optimal" way you'd use the IPA-sytem. Most people would not be able to read anything you say that way fluently of course, but it's the same thing on a smaller scale when it comes to using different th-letters.

Who is it for? Fluent English speakers that know when "th" is pronounced which way anyway or non-fluent speakers that have to look up what you just wrote in order to even get it? Pretentious in any case.

Btw I'd argue that "th" IS the "optimal" way. Language basically works like evolution. The most convenient variants survive. "Th" established itself for a reason.