Alright, I have done some scientific research to conclude which one console is the one to have to play the classic arcade games from the "Golden Era." The consoles I compared were based on input from this thread: Atari 2600, 5200, 7800, XEGS, NES and Colecovision.
Below is the list of 41 arcade games I chose to base this analysis. I used the book Supercade as a reference of significant releases in the era:
Asteroids
Berzerk
Breakout
BurgerTIme
Carnival
Centipede
Circus
Defender
Dig Dug
Donkey Kong
Donkey Kong Jr
Frogger
Galaga
Galaxian
Gorf
Joust
Jungle Hunt
Mario Bros
Millipede
Missile Command
Mouse Trap
Mr Do
Ms. Pac Man
Pac Man
Phoenix
Pole Position
Q*bert
Robotron: 2084
Satan's Hollow
Sea Wolf
Space Invaders
Spy Hunter
Stargate
Track & Field
Turbo
Vanguard
Venture
Warlords
Wizard of Wor
Xevious
Zaxxon
Next, I researched the number of native ports per respective system:
2600 35
5200 20
7800 12
XEGS 13
NES 10
Colecovision 20
Lastly, I used videogamecritic.com to determine the quality of these ports. Where there were omissions (which were only a few), I made interpretations from the reviews in the book "Classic Home Video Games 1972-1984 A Complete Reference Guide" by Weiss.
The average grades for the respective systems are as follows:
2600 B
5200 B
7800 A-
XEGS A-
NES B
Colecovision A
Based on this information, if you had to own only on console, that console would be the Atari 7800. Although the Colecovision has the same number of ports and a better average grade, the 7800 hardware is less problematic than the Colecovision. Also, there is no need for a separate module to play the 2600 cartridges.