I am pretty sure that there is absolutely no difference in the authorization tokens with keychain. That is the entire idea behind both SteemConnect and keychain. In both cases the key owner is the one that has the actual passwords, but you are giving authorization. Never of them remove the authorization for you when you leave the site. So Keychain and SteemConnect are equally as safe in these terms.

SteemConnest has a much longer track record of proving it's safe, but I fully trust Keychain also. Just not a fan of Chrome.