I bought a replacement battery from ReplaceBase for a mid-2012 MacBook Pro a while back, the ‘OEM option’. Battery utility shows it as a Simplo battery, which is indeed one of Apple’s OE suppliers apparently, and it’s been fine for me. I have no idea if it’s comparable to a genuine Apple battery, but like I say it’s been fine.
This was after a lot of wading through eBay and Amazon and looking for some sort of credible review online. The Newertech batteries do seem to get decent feedback, but are proper expensive. The one I bought was around 40 quid or so, but seems to have been a decent balance between cost and performance.