How do you choose scales to solo on when playing twelve bar blues?

In this case, I'm playing the A-D-E 12 Bar.

While this is really a preference issue, the "Purest" sounding blues scales tend to be the minor pentatonic, Blues scale (Minor Pentatonic with a flattened fifth added), and the dorian mode. In all honesty though you can really turn some heads by taking a jazz approach at a blues solo. Try combining several different scales and modes or throwing in a few chromatic passing notes to hear a little something different!

i like to use the dorian moad

it depends on the instrument you play I'm a harmonica player and I play the fourth scale up. For example, if the song is in A I play a D harp. Guitar and piano usually play on key but in different registers.

Blues scales- learn them in those keys and go to it!

it is personal choice please your ears ...........

You need more practice. Sorry, but the scales are already chosen, you need to learn to "speak" the language. There are basically 5 positions in the typical blues scale, that get you fron the nut to the 12th fret ( in E of course ). Learn these positions on the fingerboard. I can improvise a blues solo, and talk to someone at the time. But, I have been soloing for 42 years. The harder you work at truly knowing your scales, the more obvious it all becomes. Good Luck.

This the blues man, your breeding to much into it. The scales are already there. Learn them inside and out and then PLAY FROM THE HEART. Its blues not classical, jazz or fusion. If you play how you feel then your playing it right. A great man once said " the blues ain't nothin' but a good man feeling bad". Now you be here every Saturday night at midnight, and you learn them blues.

There are basicly five positions for a blues scale and the general rule of thumb is four fingers, four frets. For range, you can play above or below the tonic. Generally b3, b5, b7 notes are used based on a major scale. Modes like Dorian and Mixolidian, as well as penatonic major and minor scales can work well. I play by ear as though music was a langauge and I just go with what I want to say and tend to mix it all up and play counter point to the notes in the key the band is playing in.