You're in luck — there's a large and varied English-language historiography on Spain (though obviously if you can speak/read Spanish, that opens a lot of really interesting doors for you.)

You're not wrong that there's a lot of ideological contention, and that extends deep into the historiography too. So 'caveat lector' applies to pretty much anything you read about the civil war.

My go-to single-volume history is Hugh Thomas' The Spanish Civil War. It's a little dated, but I think it's still the single best standalone history of the war that's been published in English.

Other mainstream survey texts worth consulting:

• Paul Preston — The Spanish Civil War: Reaction, Revolution and Revenge
• Antony Beever — The Battle for Spain: The Spanish Civil War 1936–39
• Gabriel Jackson — The Spanish Republic and the Civil War 1931-39

There's also a great deal of specialist literature on the civil war and its aftermath, so if there's a particular area you're interested in, you can almost certainly find it covered in the historiography.

In addition to /u/k1990's selections, I would add in an echo recommending Hugh Thomas, and Stanley Payneis another authors with a good one-volume history of the war. For atrocities during the war, Paul Preston's The Spanish Holocaust is excellent (despite its poor title). For the anticlerical side of the atrocities angle, Jose Sanchez wrote The Spanish Civil War as a Religious Tragedy which is an excellent companion piece to Preston's work.

I also found the autobiographical Escape Via Berlin by Jose Antonio Aguirre (the exiled Basque president) to be fascinating not only in retelling his unlikely exit from Europe but also in giving insight to the man during and following the Spanish Civil War.

If a book portrays the Spanish Civil War as a "Crusade," avoid it.