I use Rosehosting to host my business websites for more than 2 years and I'm still impressed with their level of courtesy and professionalism. There are many things about RoseHosting that I really appreciate, including excellent server security and stability, no overselling of bandwidth or disk usage, 99.9 % server uptime etc... but the key factor that always amazes me is the customer/technical support they offer. They have helped me on numerous occasions even when I was the blame for the problems in the first place. Very knowledgeable, polite and patient (which in my case there was a great need of patience from their side since I am a noob for Linux administration), they are even going out of their support scope in order to help me. Also, RoseHosting tech support guys are always available, even on weekends and holidays.
Performance wise, I noticed that my websites are a lot faster after I started to host with them. My load time used to be around 4.5 seconds, and subsequently it dropped to 900ms (tested using pingdom tools). Everything is running very smoothly and fast.
They are a number one company in the web hosting market. I highly recommend them.