This might sound a silly (probably it is!) question to ask. But whenever I go to give a talk at some other institute I face this dilemma of putting the host institute's logo or only my affiliation logo, on the title slide. Most of the time I put both.
Keeping aside my decade-old-hesitations, let me ask you about your opinion on this.
The acceptable use of logos is usually described in an institution's corporate design manual. The corporate design manuals I've seen do usually not allow people not affiliated with the institution to use the logo without explicit permission, so I would never use the host institutions logo. Such thing will also not vary between fields (in my university's cd-manual, only some color schemes differ between faculties). There might even be some legal issues involved, but I'm not competent to discuss legal matters.
Most academics in at least my field, quite reasonably, ignore corporate design manuals which might even specify minutiae of how your slides are supposed to look. Usually, they do this by not showing any logo at all- my preferred choice for aesthetic reasons. But there is absolutely no reason to show a host university's logo.
Use either, neither or both.
In an academic context, this sort of thing doesn't matter (and, as StrongBad says, it's perhaps unusual to put the host's logo on your slides, although probably not a faux pas).
Focus on more important things like the content of the talk.
