Steam is 2€ cheaper but are there any other advanteges?

DRM Free is always a huge advantage to me especially for old games even if I were to pay a little bit extra, but its up to you really :)

GOG has a ton of extras. But I imagine the Steam version should come with a manual. I really like how I game with Steam but GOG has been really great with the Oldies and I have yet to have a problem with a game.

I own both, the Steam version runs hyper fast, you hit the key to move and you run across the room at lightning speed. Haven't noticed that same issue in the GOG version.

Running Win 7 x64

You don't need Steam!

Using Steam is like buying a car, but having only the rights as if you leased it, in addition giving the merchant the right to control your drivers log, monitoring your car and the parking place and every time you plan to drive the car...you have to ask for permission.

Well. Obvioulsy on this forum you will meet people who prefer the DRM-free alternative before Steam's one.

So, I would say that the DRM-free installer alone is worth the money. Plus extras.

But I must say that when it comes to older games, GOG does its homework, while steam doesn't. My experience with commandos and steam is: google the fuck out of a patch. My experience with GOG with all games but one (and only because I updated my graphics card): runs great.
Also, GOG support is very quick and efficiente, while Steam's one doesn't care as much for older games (or cared).
And you can add the game to steam as a no-steam game if you want your friends to see you playing and stuff.
So, I'd go with GOG, specially if so little saving is the only advantage to GOG.

For me, it's a matter of principle. Do you support GoG's policy or do you support Steam's?

Warning: Incoming semi rant

For me, its GoG hands down but this is a biased comment because my first and only experience with Steam was when I got Half Life 2 shortly after release. At that time, Steam was about as user friendly as a junk yard dog. After installing Half Life 2, instead of being able to play the game, I had to sit through mandatory updates which really soured the experience. I thought Amazon sent me a faulty CD so I sent it back requesting another only to find out it was a "feature" in the installation. At that time, I only had access to a dial up connection to download several hundred megabytes. I ended up leaving the PC on overnight and hoped to hell the connection wouldn't get interrupted and that was just the updates for steam. After the Steam updates were installed, I now had to update Half Life 2 and leave the computer on again for a second night. Tried running the game without updating but Steam wouldn't have any of that. After getting everything updated, still couldn't start the game because I had to be online which was also a pain. Apparently you could turn it off, sometimes it worked, sometimes it didn't. I found my internet speed was worse too because Steam was always sending packets of data home. I checked the option for steam to stop that to save bandwidth but Steam was still transferring data. In the end, I tried to finish Half Life 2 as quickly as I could to get Steam off my computer.

I don't care if I haven't used a dial up connection for a while, I don't care if the most updated games give the best experience (potentially making my saved incompatible), I don't care about online achievements and I don't care about features I'll never use. If I can't use the software I bought without you telling me how and when I can use it, then you should be paying me to use your service.

After finishing half life 2, I uninstalled it, uninstalled steam and got a pirated version of half life 2 instead. I'm sure Steam has changed a lot in the last 10 years so I don't know what it's like now but I just can't be bothered trying it again after such as intrusive experience.

Rant off

Edit: @OP, another thing you might want to consider is if you want to mod your copies of Deus Ex. I don't know how mod friendly Steam games are but logically, with mandatory updates, it seems likely game files could be corrupted. Keep in mind I've never tried this so it might be better to ask on the Steam forums how mod friendly Steam games are. The Fallout games and System Shock 2 I can't imagine playing without mods so for me, the assurance that I can safely mod my copy of Deus Ex without Steam wreaking my games with updates are a plus. Not sure if this scenario is likely as I don't have the experience but if you want to mod Deus Ex, I would ask on the Steam forums how safe your game would be.

I find funny how natural criticism is now treated as -rant- another achievement of Steam I guess.

The IwubCheeze's comments explains some of the points, you do not use Steam. Steam uses you and put digital handcuff on you and the software you want to use...

From what I've seen of Steam's policies I've come to view it as yet another American bully corporation.

Also, GOG's customer support is pretty top notch. You get that when you buy the game here.

There's no doubt in my mind that the GOG version is well worth it, and in fact heads and shoulders over the Steam offering.

Buy Steam when there's no alternative. And then only after thinking about it long and hard over a weekend.

Buy the GOG version of Deus Ex, it's one of the best games ever made and you deserve to own it, not just "rent it".

Gog 100%, you get extras, the OST, etc. And you're owning rather than renting

I'd go with Gog as well. They offer more extras, DRM-free, and it's a lot less work to optimize the games.

For instance I bought Fallout series on Steam a few years back. Took a few hours to get all the high-res patches working, and then they suddenly stopped working after 10 hours of gameplay. Bought on GOG and haven't had that issue.

Steams great but I'd go with GOG on this one.

Well, it is half true...

The advantage of the Steam version is you get the original GOTY edition.

The disadvantage of the Steam version is you get the original GOTY edition... bugs/features-and-all. If you are on a modern machine with something later than Win7 you are likely to need to apply the Kentie launcher (patches, and dx9/10 renderers {gog won't let me post any links] ) to avoid speed issues and avoid the need to run as admin to save to the Saves directory. I believe the gog version is pre-patched with the fixes needed for Win7 multi-core/cpu machines unlike the original GOTY version v1112fm.

I understand the GOTY edition from Steam also has map bug and an end of game bug - look for deusexv2 on code.google.com

I own the cd version of Deus Ex and Steam. I do not own the gog version, if I was to do it again I'd probably go for the gog version for an easier install and go experience.

GOG also has the "Game of the Year" edition, but that doesn't really say anything. "GOTY" is just the retail game with the multiplayer patch. It has been out for years in bargain bins under the Ubisoft Exclusives label before coming to Steam and GOG.