Amstrad (Schneider) CPC 6128
Although Amstrad CPC is not the preferred choice among vintage computer fans, it’s definitely a very interesting series of 8-bit computers and was sold in millions of units. This model combines 80-column display (screen resolution of 640×200), integrated 3-inch disk drive (each diskette can hold 360kB of data), AY sound and surprisingly good keyboard.
This was one of the cheapest computers that could run CP/M, the operating system with many professional programs available. Although Wikipedia says that there were a lot of games on CPC computers, I saw only people using this machine for actual work. This particular machine was used in the late 80s by a scientist in a geophysical institute for simulations and word processing. He sold the machine with an 5.25-inch external drive (made by Robotron and modified to work with CPC), an RS232c interface and a box full of disks containing development tools, his own Pascal programs and a customized version of WordStar (that allowed users to write and read Czech characters).
The keyboard is better that those on 8-bit Atari and Commodore computers and the computer gives more professional overall feeling. I like how CP/M has been integrated in the system. You can easily switch between BASIC (AMSDOS) and CP/M environments by using |CPM and AMSDOS commands and both use the same way to store files on disks.
I know that it is possible to run CP/M also on Spectrum +3 and Commodore 128. However, the former supports only 40-column display and the latter is significantly slower due to hardware design limits. This was a better choice for those who wanted to use CP/M on a home computer back then.