The Apple II was special because it was released in 1977 with bit-mapped color graphics and sound. The Apple Disk II disk drive was released in 1978. Being a few years early with an all-in-one computer with a fast disk drive, bit-mapped color graphics and sound gave the Apple II an edge over the others. Five years later, Commodore released the low cost Commodore 64, and Apple no longer had the edge in the 8-bit market, but did have significant market share.
Radio Shack TRS-80: 1977 mono-text (Z/80)
Commodore Pet: 1977 mono-text, VIC-20: 1981, Commodore 64: 1982, Amiga 1985
Atari 2600 game console: late 1977, Atari 400/800: 1979, Atari ST: 1985
Acorn System 75: 1979
ZX 80: 1980, ZX 81: 1981, Spectrum: 1982
CP/M operating system: 1973-74, S-100 bus: 1974, Altair: 1974
Those CP/M "business" machines, CP/M (Z80) and 80-column cards that you could plug into the Apple II, and then the IBM-PC was released in 1981.
Apple Lisa: 1983 mouse mono, Mac: 1984 mono 3 1/2" disk drive, 1985 AppleTalk networking
If you look at market share before the IBM PC, Commodore actually owned the market.  Looking at the graph from http://arstechnica.com/business/2012/08/from-altair-to-ipad-... Commodore peaked in the 80's (Commodore 64 launch). Apple wasn't the market leader, but probably made a lot of the profit.
The Amiga is not really of that era but is really a successor in spirit and technique to the Atari 8-bit computers (Jay Miner again). It is definitely a superior machine to the same eras Macintosh (Macintosh 512K vs Amiga 1000).
Over time, the simple design of the Apple meant it could be added to, and it's programming environment was very friendly.
Truth is, I learned 6502 assembly, and various languages on an Apple 2. The ROM code listing was right there, so was the schematic. That open nature meant people could open the box and just go.
Atari machines are capable, and fast, but...
They don't do that out of the box, and it took people a while to really exploit the things.
Apple got 80 column text, and it got cards for all sorts of things. Heck, I'm working on one myself. Always wanted to, so why not?
That expansion capability meant an Apple 2 made for a great 8 bit workstation, and an awful lot of Atari related development happened on the more usable Apple 2.
I think the technical capabilities of machines like the Atari were really noteworthy at that time. But, the Apple 2 did just enough. 6 colors on the high-res screen, for example, was just enough. You can do anything in 6 colors, but it's harder to do it in 4...
Today, I can fire up that machine, write some stuff, save it to a USB thumb drive, plug that into my PC, get the disk image open, get the data and go. Spiffy, if you ask me.
> They don't do that out of the box, and it took people a while to really exploit the things.
I never really had much problem programming the Atari, the Apple II was simpler but it sure is a less capable machine overall. Music and graphics are pretty simple on the Atari once you get the hang of it (which I don't think takes very long given the right book) and you can do things the Apple just cannot do.
Having 80 column text, a nice office type suite, lots of expansion options: test & measurement, industrial control, etc... made an Apple quite a nice machine.
In terms of entertainment, games, etc... yeah. Totally. Though I have to admit, many of the greater game experiences on an Apple are pretty darn great. But, there were a ton of things done on more capable machines with custom chips that were better. No argument.
But, when it came to getting shit done, making money?
I made a ton of money with an Apple computer. Money that was off the table with the Atari one, unless I was going to write a killer game. Plenty did.
But plenty more did things that were not so much entertainment too.
I love my Atari machine and spent long hours on it making it do all sorts of spiffy things with graphics and sound, and I really loved the bi-directional game ports. It is a nice machine.
We need to be careful about "less capable" in this context though. While I didn't spend the same hours on that Apple in the same way, because the simpler design didn't require it, I did spend them getting lots of things done for people, and for myself. Often somewhat boring things, compared to fun graphics and sound, but important things. The software was there, storage etc...
As far as the hardware itself, it really doesn't compare to Amigas and 32-bit Ataris and so on. It managed to stay popular a long time by providing a software ecosystem that people were comfortable developing for and buying into and by Apple's courting relationships with schools.
True for me.
Most of us got something else at home. For me that was an Atari, but I wanted an Apple. The Atari had fun chips and it was fast. But the Apple, well equipped, was a workstation, and that little difference meant a lot to some people. Others not so much.
Depends on games, programming, etc...