You're probably best to phone them direct. Peoples opinion will differ. One persons hard is another persons soft, ooh ah!? For a road car I'd say don't go too hard. You can usually swap out the springs for the next ones up if you do fancy going stiffer in the future. If you want to go low fit adjustable alignment arms. To cure body roll fit some uprated ARB's. To cure the floaty rear end fit polybushes in the subframe. To cure that soggy steering feel fit poly rack bushes. To make the biggest difference get it corrected and setup at a wheel alignment specialist. And so on
Edit: BC are a good choice. I have their ER series fitted to mine and they're great. Had Apex Gen II's before that were also pretty decent. Were still going strong 5+ years later when I sold them on to someone else. With both sets of springs, I believe