Hard to recommend a good 8-bitter from good old times. If you had a C-64, you will recommend it, same with the 8 bit machines from ATARI.
The built-in BASIC-interpreters are often crap in my personal opinion, this is valid especially for the C64 (BASIC V2). The ATARI's (800XL, 130XE, 65XE) were slightly better.
Forget about the Commodore Plus 4
The king was C64, simply because most games to play were developed for this machine.
ATARI was better in my opinion but never made it to beat the C64, good software, not only games.
Sinclair ZX Spectrum was good machine, worth a look too. But good software is very rare...
First recommendation is an ATARI (one of the three above) with TURBO-BASIC-XL. The best BASIC I've ever seen. All is possible, even faster when compiling the TurboBASIC-Code with the compiler.
Second recommendation is the Commodore C128. You can switch between C64 (BASIC V2) and the much better C128-Mode (BASIC V7). Additionally you have the chance to run that machine in CP/M-Mode, this is compatible with early MS-DOS-Versions.
Depends on what you want to do. C64 has the better soundchip, ATARI the better GRAPHICS and structural design.
The 6502-processor of the ATARI's and I think the 6510-processor of the C64 too have a buswidth of 8 Bit. 65XX was the first processor with rudimental pipelining. The bad thing were the registers. Not 16 Bit, it was switchable double 8 Bit. But this is nice to know. You want to program in BASIC, not in assembler. And keep in mind, there is a limitation in RAM. Not really 64kByte are available, see the blue picture in the first post...
It is simply a wide field of early computing technology, but it was pure fun. Everything was possible and I miss that times...