Unfortunately, there is no best strain for any condition: Anxiety type and intensity; migraine frequency and intensity; tolerance to THC; and amenability to psychoactive effects, are just a few of the factors to consider when formulating a treatment plan.
I recommend that you try a few different CBD strains. The "Very high CBD strains" would not cause much, if any psychoactivity, while the "CBD strains" would likely be more effective at reducing anxiety levels, and at reducing migraine frequency, duration and pain levels, but would cause mild to moderate levels of psychoactivity.
Here are a few recommended strains to consider:
Very high CBD strains
ACDC – a 20:1 sativa strain
Ringo’s Gift – a 25:1 hybrid strain
Charlotte’s Web – a 30:1 sativa strain
Harlequin – a 5:2 sativa strain
Sweet and Sour Widow – a 1:1 indica strain
Pennywise – a 1:1 indica strain
Cannatonic – a 3:1 hybrid strain
I hope this helps!