Hi Ann Marie -
My niche is also relatively small (geographically speaking), and I also have the issue that not all hotels/motels in my area are on TA. But I've found that, with a few exceptions, the hotels/motels that aren't on TA, aren't on the other booking sites, either.
I can't tell you about my experience with Trivago, because I've never used it on my site. However, I did check out Trivago's affiliate program some time last year to see if it'd be worth switching from TA to Trivago for my hotel and motel listings. (I don't use TA for my vacation rental listings.)
I decided to stick with TA, primarily because I liked TA's commission structure better. If memory serves, at that time Trivago's affiliate program would pay me a flat rate (40 cents?) for every click from my site to theirs; whereas, TA pays me 50% of the revenue TA earns on each "commerce click" referred from my site.
From what I could figure looking at my analytics for TA, I came to the conclusion that I'd likely make more from TA's 50% than I would from Trivago's flat rate.
The other thing that made me stick with TA over changing to Trivago was the large number of unique TA deep links I have on my site. It would've taken me a ton of time to change them all to Trivago links. So I made the executive decision that it probably wasn't worth the effort to make the change, just to see if I could earn a few more bucks a week with Trivago's flat-rate-per-click commission structure.
Sorry I can only give you my general assessment about TA vs. Trivago, rather than any hard evidence one way or the other. Maybe someone who has experience with TA and
Trivago will jump in and educate both of us. Let's hope so!