On WH Smiths, their customer facing stores just seem to be in 2 minds as others have said. Their travel stores in stations airports are doing well, and I use them fairly often (buy a newspaper/magazine for journey, and maybe a bottle of water and a snack). But the high-street stores however are dire and I only go into the local one for the post office it has in the back, which is the only area they seem to attract customers.
Boots is safe in my opinion. While they might not seem it, they actually specialize very well in several areas (which is v tricky to pull off). For most places I've been to, boots is the main pharmacy on the high street, with a wide range of off the shelf or over the counter products (as well as prescription services). Then on the other side, they are also one of the biggest high street cosmetic sellers. Not the high end stuff, but still a good selection from cheap make-up to fairly pricey premium brands. There is only one company really challenging them on the high street and that is:
Superdrug (who get my vote for next to fail). Superdrug seem to try and do the same as boots, with a mixture of pharmaceuticals and cosmetics, but they just seem to do it in a cheaper tattier way (and only a few of their stores have actual pharmacies). I only go there as a last resort if for some reason whatever I want isn't in boots.