Many people feel difficult to type the the circumflex letters. Since very beginning of Esperanto development, people start to use different ways to replace those letters. One common solution is X-system by adding x. So the new letters look like cx, gx, hx, jx, sx, ux, etc. Another solution is H-system, by adding letter h, to form ch, gh, hh, jh, sh, etc, ŭ same as u. The latter was rejected by many people since h is an existing letter and merging ŭ and u causes some ambiguity. It seems X-system is preferred by most groups, in internet and prints when the circumflex fonts are not available.
Personally I dislike the X-system. It breaks the normal word form in a weird way and makes the appearance un-natural. The alternative system is just a temporary replacement and it functions to bring people convenience not to add more discomfort. There might be another way of using apostrophe ' instead of x, which actually makes it worse.
As per H-system, I prefer the adjusted version, ch, gh, kh, zh, sh, and w. It is not the straightforward way to add h to form new letters, but the spellings match the traditional use of Latin letters and are easy to read. Almost all people could understand immediately what they represent in circumflex letters. I ever thought of using y instead of j and, using j to replacing gh, etc, but that changes too much and add more potential ambiguity. Currently I stay with the adjusted H-system mentioned above.
Which way are you using when circumflex letters are not available from your keyboard?