... such as the AT89C51RD2/ED2 is, that it can be uploaded via a serial port very comfortably. It means, that you don't need a device programmer to burn an EPROM, nor a not-too-reliable "cable" to the parallel port (for the AT89S')(not to mention that parallel ports are hard to find on modern PCs anyway, while USB-to-serial "cables" are readily available). There are more benefits of this but I won't go into the details now. You can still use a ready made board or anything - the 'RD2/'ED2 is fully pin compatible to the oldies - the only "extra" you might need to modify is a jumper to a pulldown resistor on the /PSEN pin, to facilitate bootloader entry. Or, alternatively, get the NXP (ex-Philips) equivalent, the P89V51RD2, that won't need even that pulldown (but has less on-chip RAM, regrettably).

I would not spend a halfpence on a maskROM based B52 chip, once the hexfile is freely available on the Internet. The extra benefit of a FLASH based device is that you can then burn ANY program, not only the BASIC interpreter into it, if you later decide to move beyond BASIC to the "real" programming.

JW