Both are good. Bluehost offers good technical support, while HostGator has a little bit better servers. Although I can't support a company whose entire business model revolves around false advertising. (Inflated claims of storage/bandwidth) If you understand the business and aren't really looking to use an entire hard drive on a shared server though, and you read the TOS for both companies carefully, they both provide good service for the price (as do most hosting companies).
I am using Bluehost and I love it. Haven't tried Hostgator but Bluehost is really good. The only problem with Bluehost is that you get only 50 MySQL databases, while you get with Hostgator unlimited.