I've got the option to carve out 20 or so acres from a few hundred, and I'm curious what part of it is best when it comes to pond construction(if any of it is). I mapped it with the web soil survey, but I don't really know how to read the data. I'll paste the soil types below.

Map Unit Symbol Map Unit Name Acres in AOI Percent of AOI
7 Austin silty clay, 1 to 3 percent slopes 84.4 14.4%
8 Austin silty clay, 2 to 5 percent slopes, eroded 19.0 3.2%
24 Chatt clay, 1 to 3 percent slopes 1.1 0.2%
34 Eddy very gravelly clay loam, 1 to 3 percent slopes 67.7 11.6%
35 Eddy very gravelly clay loam, 3 to 8 percent slopes 0.5 0.1%
37 Ferris clay, 5 to 12 percent slopes 12.7 2.2%
39 Ferris-Heiden complex, 2 to 5 percent slopes 81.3 13.9%
43 Heiden clay, 1 to 3 percent slopes 88.0 15.0%
48 Houston Black clay, 0 to 1 percent slopes 36.8 6.3%
49 Houston Black clay, 1 to 3 percent slopes 45.2 7.7%
54 Krum silty clay, 0 to 1 percent slopes 1.0 0.2%
70 Stephen silty clay, 1 to 4 percent slopes 66.0 11.3%
71 Stephen silty clay, 3 to 5 percent slopes 1.4 0.2%
72 Sunev clay loam, 5 to 15 percent slopes 53.9 9.2%
78 Venus loam, 3 to 5 percent slopes 25.1 4.3%
W Water 1.2 0.2%
Totals for Area of Interest 585.4 100.0%

I'm wanting about an acre of water, so a pond liner is really out of my price range. Am I looking for a certain type of soil, clay percentage, etc?

I'll offer some thoughts about this.
First, there are more than 50,000 soil types in the United States.
You can try to read these soil surveys until the cows come home, but until you dig some holes and figure out "plasticity", you won't know if your dirt will work or not.
I'd call Mike Otto and talk to him about your soil types, where you are located in Texas, and he'll help guide you through the best process (940)665-2258.
Otto has been an earthmover more than 40 years and understands dirt better than anyone I've ever met. He'll steer you in the right direction.

Jose, let me second Mr. Lusk's remarks: Get in touch with Mike Otto!

Mike was busy doing another project when I called him two years ago to check my soil, but he came down anyway to take a look. After tramping around a bit, he declared my red clay hill to be mostly iron oxide (hence the red) and sand, totally unsuitable for holding water. If not for him, I'd have bought the land under a completely wrong idea and not found out until too late!

Fortunately, I did eventually find good clay, though nowhere near the hill. But you don't know for sure until you dig and an expert takes a look!

Jose, Mike has written the best book on pond building that I've seen. "Just Add Water" is worth many times the cost. Especially since you are doing a 20 acre one.

Thanks guys, I left him a message.

I did some more research and the spot I want is actually not that long list, it's just 85% houston black clay.

How deep that goes or how accurate that information is, I have no idea.

https://soilseries.sc.egov.usda.gov/OSD_Docs/H/HOUSTON_BLACK.html

After using the maps, enter the soil name(s) in the Official series description link. It'll give you more detail about the soil series.

If this was mapped accurately, you have a clay textured soil (40% or more clay), it is an expansive type of clay, and very plastic.

I 2nd what CW said about the soil surveys. The corresponding information after being mapped out should convey what the series is, i.e. what the soil profile looks like. I've used this before for looking into duck hunting ground (ground that will hold water at least 3 months of the year).