Buying Old Consoles - Which old console is better for now ?

I liked Sega Mega Drive II when I was young :)

First of all check games on which platform you want to play more. Should answer the question.

Nintendo DS

I loved to play sega master system II, snes and ps1

I prefer PS2, Dreamcast, Megadrive 2 and Nintendo64

PS3 FAT, because of native hardware PS2 emulation.

NES all the way

Depending where you are you can get a modded ps3, that can then play most ps2 games as well

Dreamcast
Unique library, aged well, has some neat gimmicks

You could just use emulators for the older consoles. There are emulators for PS2 and PS3, albeit I'm not sure how far PS3 one has progressed as I haven't tried it out (too busy with the games I have on steam).
Games often look better and run at better frame rate on emulators, not to mention you can customize controls as you see fit. They're by far superior than actual consoles themselves.

Personally i would suggest ps3 slim if only just for sake of hard drive which ps2 lacks. Save memory cards are kinda pain in the ass.

On other hand you might want to consider what games you're after, and get the one that has more games you want?

I'm a Nintendo guy (never had an N64 and not intererested in the Switch) so I'll go for SNES (original) > DS (lite) > Wii (slim)

Mega Drive

There are emulators out there for most of the consoles, but not (the last time I checked) for Xbox. Make of that what you will.

I myself own an Xbox 360, Wii and a Playstation 2. I can hopefully add the N64 soon because I still have nostalgic feelings towards that console because of my childhood. I still have a distant wish of adding the Snes and PSX to my inventory as well. For me, the feeling having these tangible items in my home really gives me a good feeling! However, the choice of what old console you should buy depends on the games you like most. I would browse different websites such as IGN or Gamespot to check out the reviews. Probably this can help you choose an old console in combination with games that suit you best!

colleco vision with thhe game "B.C.'s Quest for Tires"

I'd say a PS3 because you can mod it. I've also got a PS2 somewhere to play PS2 + PS1 games, but I haven't hooked it up in a while.

20GB or 60GB launch PS3 is the best if you keep it cool and in good condition. I have lots of consoles (including four PS3's, two 60GBs) so I feel have a wide perspective of what is out there and their uses and the launch PS3s that play PS, PS2, and PS3 discs, as well as have a digital store with PS, PS2, PS3, and even some ports of PSP games, along with free online service is the best general purpose gaming console that I own. You have to take care of them though, I have two 60GBs because one doesn't really work (that I got cheap) and needs to be torn down and repaired, which I'll do later this summer. Keep them ventilated, not in a closed off cabinet or whatever, and perhaps an additional fan and they should be fine.

You guys are great and I think I'll get a modded PS3 FAT this summer

N64 - got me so many childhood memories. Awesome stuff.

SNES if you want something good but with already a colour palette.
Dreamcast if you want one of the strongest libraries ever.
PlayStation 2 if you want the last real console not made by Nintendo.
Wii if your idea of old is "around 10 years old".

Everyone have a different background so there will be no generic "better". I fell in love with the Super Nintendo (Zelda, Secret of Evermore, …) so it would be that. I guess it's more about games than a particular console.

Terminator 2 aka Super Design Ending-Man BS-500 AS. I still have it working and this doesn't break, even after multiple punches from me and friends from when I was a kid... Darn... 15 years have passed...

Nobody said Gamecube yet? well, here you go!

pcsx2 it's your emulator :) enjoy it.