According to WPATH, order is optional. In my situation, I knew HRT was easier to obtain through my insurance, so I went for that first and my doctor had no objections. The other way around would have been a bother when top surgery wasn't covered, and some places won't let you have top at all if you haven't been on hormones for a given amount of time. So really, it depends on cost, which is bothering you most, what's available to you, etc. Lots of variables that are hard to tell without knowing individual situations.
Sorry if this wasn't much help, just stuff to think about, I guess?