For a standard road bike ?, I’d rather have external, but also the ability to put Di2 internal.

For a gravel bike, rather have internal as less dust and dirt in the housings. But I’d want the b-bracket to have one of those nifty screwed on covers that gives you access to the down tube, seat tube and right chainstay. I’ve seen that on some Chinese carbon gravel designs. In theory makes life much easier.

On a mt. bike, internal again. My new Specialized HT has 1X with the shift cable internal in the down tube, then external on the chain stay. As it’s full length housing, pretty easy to route new.