So I've got this Google MyMap with about fifty Hill Country access points marked on it, gleaned from fly fishing books, forum posts, and the like. I realize now this is far more than I'll ever be able to visit. But I do want to take the fly rod and a pair of swim trunks out there and get myself a few good weekends of fishing. What river should I concentrate on? Llano? Guadalupe? Lampasas? Blanco? What's y'all's favorite?

all of the above, good luck

San Gabriel

I do not fly fish but fish the hill country a lot every year. I have some pretty good places both public and private. Love the Guadalupe with the Blanco and Llano holding second and third. I also love the Sabinal Valley and Nueces Canyon. Plenty of creeks both in the valley and canyon. Friends of mine who fish only on the fly love the Llano River the best !

Okay, that's actually widened my options. I guess I'll just have to fish them all.

You will not go wrong!

The San Saba River downstream of Menard is very fishy, just hardly any access points. We stayed at a private campground years ago and caught a lot of crappie, catfish and bass. The San Saba there is a series of deep pools usually with intervening small rapids. Look at the satellite views, you will see what I mean. I don’t know if it is considered a navigable river by law at that point.

The South Llano River from Telegraph to the state park is clear and deep in many places, full of the indigenous bass. Very canoeable. The Medina River below medina is nice when the water is flowing high enough.

My experience with hill country rivers and creeks is if they have deep pools that survive the inevitable droughts, they will get some good fish in them. Even little creeks can have some deep pools. If they are navigable by law, then you have a legal right to fish there. I don’t know if the state has a list of all the navigable waterways. Would be nice if they did.

@karstopo, even more ideas, thanks!

A cursory duckduckgoing of the list of navigable waterways question gives this page from TPWD:
https://tpwd.texas.gov/publications...s/navigation/kennedy/kennedy_faq.phtml#I
"Texas courts have the final say over this question, and there have been several cases recognizing particular streams as navigable or perennial, and therefore public. But there is no master list."
Then it goes on to suggest that you check the county courthouse to see if the local land grants originated from Spain or Mexico. Looks like streams hover in a Schrodinger-cat-like limbo between navigable and non until someone actually ends up in court.