OCTGN probably has the best one, but it is the most "difficult" to learn. Took me a few tries but now it just makes sense. You can filter through cards by almost everything, and if you subscribe (as low as 3 bucks a month to get rid of that annoying subscribe banner!) you can save your filter searches and what not.
On the other hand the forum builder is very good as well. It's a bit easier to use but it's limited in availability, in so far as no promos appear available here. But the point and click GUI and the constant visual card and SP counter is very useful for scatter brains like myself. And it's relatively easy to transfer a book from here to there and vice versa.
However the companion app builder, though amazing upon release, hasn't been thoroughly updated in a while, and only filters cards by school and a few other criteria, leading to more fishing through screens of cards till you find the one you want.
All that to say coshades correct, if you can learn it, the OCTGN builder has the most options and most flexible way of using it. Good luck!
