Texas has gotten a lot of rain in the last few months. I wouldn;t worry too much about lake levels on Austin. To me it would come donwn to whether you want to camp out in the sticks or near a metropolitan scene with nightlife potential.
I lived in Austin for about 13 years, and loved camping at City Park (Emma Long) and grabbing that early butter, but I have never been out to Amistad and would love to check it out. Travis is bacck up too, so you might check out hitting the Pedernales as well.
If you consider the Trinity, check the release levels of the upstream lakes. Lewisville is still letting out a lot of water, and all the crap it washes out goes down stream. It is supposed to be a wet spring, so that destination might be a bit risky in terms of having ridable water.