Funny thing, Atari 8-bit computers started as project that was to replace Atari VCS (2600)...but seeing how computer market was booming, Atari made decision to make computers...5200 was then return to original intent, though apparently, due to internal split between Atari's console and computer divisions, as well as how licensing worked, it was made incompatible with 400/800 line...which was really mindblowingly stupid decision.

With that said, it was easy to port 5200 games to the 400/800. A number of my games (all of them on generic floppies) were 400/800 conversions, though I didn't do them myself, of course. 

I think 5200 ended up with less than 70 titles in the end...which was real pity, since 400/800 had something like 400-500 IIRC, and they were running on practically same harwdare. I mean, if it was compatible with 400/800 it would've probably fare better, though ColecoVision was really a punch in the face for Atari at that time.

NeoGeo

I forgot that had a home version. Just as much as a contender as PCEngine. Anyone that says anything other than either Neo Geo or PCE hasn't spent much time with either system. Both are better than many modern systems. 

Atari 2600, Neo Geo CD, 3DO (The Need for Speed... )

It is funny how many consoles failed at Fifth/Forth Generation and i probably forget some :

3DO
Atari Jaguar
Neo Geo
Amiga CD32
Amstrad GX4000
Philips CD-i

Definitely the PC Engine/TurboGrafx 16 for me. Such a well rounded library of titles with both original games, good arcade ports and CD based games that would better than similar titles for years to come, all featuring splendid color. The PC Engine specifically is one of my favorite consoles aesthetically (the TG16 was a big waste of plastic and not nearly as nice looking).

Second would be the Neo Geo AES cartridge system. Fantastic visuals/audio and some great games, but not as well rounded of a catalogue as the PC Engine. Too bad the games were prohibitively expensive.

A post full of nothing but facts.

Man I really need to get around to trying out Turbografx-16, it sounds like a blast; I grew up during that generation and SNES is my #1 system of all time, so it shouldn't be too hard to adjust to. My brother actually owns one, maybe I should borrow it sometime.

For now, it's a tough call between the Neo Geo and the 2600.

The former's a 2D beast with fantastic pixel-art graphics, blazing fast performance, and badass arcade action, while the latter has that simple, back-to-basics charm.