I dont own every system ever released but i have emulators of almost every console ever released as well as thousands of games
I will have to say the 2 most underrated consoles of all time would have to be Neo Geo and DC. The Neo Geo apart from having the best collection of fighters ever (World Heroes, Samurai Showdown, Last Blade, King of Fighters, Fatal Fury, Waku Waku 7,etc) also has an impressive number of high quality puzzle games (Magical Drop 2&3, Panic Bomber, Bomberman, Gururin,Money Exchanger, Puzzle Booble, etc) and awesome shooters (Metal Slug, Pulstar, Blazing Star, Shock Troopers, etc).
The Dreamcast is a hardcore gamer paradise with lots of awesome 2d fighters and shooters. Games such as Street Fighter 3, Last Blade 2,Vampire Chronicles, Zero Gunner 2, Radiant Silvergun 2, Mars Matrix can only be found on DC. It also boasts some great racing games ( Test Drive Le Mans, Daytona Usa, MSR, Sega GT, Vanishing Point), 3d fighters (Soul Calibur, Power Stone 1 &2, Virtua Fighter 3, DOA2, Fighting Vipers 2), RPGs (the very underated Elemental Gimmick Gear, Skyes, Grandia 2, Record of Lodoss War, Silver), cool weird games (samba, typing of dead, space channel 5, Floigan Bros, OOga Booga, Jet Set Radio,Charge and Blast) awesome sport games (nba2k2, Nfl2k2, Tennis 2k2, Tony Hawk 2, Wsb2k2), survival games ( Resident Evil 2,3,cv, Alone in the Dark, Blue Stinger) fine fun for the whole family games games (sonic, Rayman 2, Puzzle Fighter 2, Mr Driller, Ms Pacman, Super Magnetic Neo, etc) and of course Shenmue 1 & 2 and PSO 1&2.
All of that quality gaming plus you can play Snes, Mame, Genesis, Nes emulators as well as online play, a VGA connection, Gun games (virtua cop 2, death crimson, house of the dead, confidential mission) keyboard and mouse support, etc, etc. Certainly worthy of being called one of the best of all time IMO.
Astro