For me, I found that 1&1's hosting services are very reliable and of good quality as well. Their staff gets back to you within 24 hours or less and they don't put you on hold for that long over the phone (which is always a bonus). Their prices are very good as well, especially considering the amount of webspace they allow you. I have been using them for about two years now and haven't found a more able-bodied provider since.

As for 100% up time, that's a rather impossible request due to the fact that there is always a chance something could go wrong. There are many with 99.9% up time though.