I'm new at this game, so take what I say with a grain of salt. But I am sending in at least three letters of rec, one from a philosophy professor, one from a Spanish professor, and one from my advisor who teaches various humanities classes.
If you read the form that LSAC requires your recommenders to include with their letters of rec, you will see that LSAC encourages your professors to include stuff about "...how the candidate will add to the diversity of the law school."
With that in mind, I think it would be best to mix it up with your letters, if possible. At least, that's the approach I took. I think law schools would like to know how you perform in different classroom settings, just as an employer might be interested in knowing how well you perform at doing various tasks that will be reflective of the job setting.
That being said, if you can't find any other professors to write you good letters, then obviously go with the four English profs.
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