The 8051 based processors have been around for a very long time. There are easily 300 different chips from about 10 manufacturers based on the 8051. You can get just about any configuration of an 8051 that you want. Most all of the support the same 8051 architecture. You will find that Intel, Philips, Siemens, and Dallas are the popular 8051 based chip makers.
Most engineers are partial to one family of chips.
The debate about which chips are 'best' is a hot button issue with many people. The important point to remember is that all chips have strengths and weaknesses. On the other hand, I am going to tell you my biased, yet very objective opinions about a few of the popular chips. The 68HC11 has been around for quite a while. It has an excellent reputation among robotics engineers because it has a good mix of peripherals such as its timer module, onboard serial ports, etc.