I've always been an author who writes what I want to write. That goes against a 'rule': authors are told to stick to one type of story so readers know what to expect in a release, which reduces the risk of alienating their audience. Alternatively, authors are advised to write different genres under different names. I think that’s good advice for writers who want to maximise their income.
I enjoy writing both historical fantasy and modern horror, and I usually write them alternately, although that's coincidence rather than planning. Maybe it’s an indication that when I'm writing one I'm itching to return to the other.
There are some exceptions, of course, such as my occasional erotica novelettes, or my World War One science fiction novel which a publisher is currently looking at. These, though, will probably remain occasional departures rather than regular genre hops.
So, which am I better (or with my modest hat on, maybe that should be least worst!) at: historical fantasy, or modern-period horror?
Feedback from readers points toward my fantasy works. A couple of readers have mentioned 'The Doe and the Dragon', set in Arthurian-period north Wales, as a favourite. Beta readers have also said encouraging things (other than having to sort an issue with my hero) about my forthcoming 'Footholder', which is also based in mythic Wales. Others like 'Andraste's Blade', which is set both in the past and the present day, but has Celtic myth and history as its base.
I think my own preference, though, is for my horror books, which I've always felt more satisfied with when I've finished them. I think that's because horror (well, mine, anyway) tends to be more straightforward, without the plethora of sub-plots fantasy works seem to need. I suppose I find horror easier to plot and write. Because my horror stories are simpler, I also tend to be more confident sub-plots and loose ends are tied up.
On the other hand, maybe it's the extra elements and deeper plots that makes readers prefer my historical fantasies over my horrors. On yet another hand (do I have three hands?), as fantasy generally sells better than horror, maybe the reader of a 'Richardson' simply reflects worldwide reading trends!