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Narrow band filters
The one you can afford!
Assuming you are going to use in on a scope infront of the camera, you may need a 2" size if you use a DSLR or full size sensor.
The narrower the bandwidth the less secondary light pollution gets through.
Ha emissions are only 0.1nm wide so either of the two will work.
It's sometimes mentioned that the narrow band doesn't work to well on fast (<f4) cones of light as the interference coatings on the filter are designed for basically parallel light beams and the edges of the fast "cone" of light go through a longer section of the coating and loose transmission; this can cause what looks like vignetting on wide fields.
Hope this helps.
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