Well lets have a look here
Graphics
Well I think it goes without saying the TS has much better graphics than the original. Take a look at some of the screen shots for the original and if you can't stand how its looks then stick to TS.
Voice acting
This is a very close call to be honest. The voice acting for the original is solid (no pun intended) where as TS makes some improvements and missteps. The most notable misstep for TS was the lack of accents for some of the supporting charters. There were also had some lines that were changed for no apparent reason. However TS did improve a little bit upon some of the main characters like Solid and Liquid Snake. Overall I wouldn't really say you are getting significantly better or worse voice acting by choosing the original or TS.
Music
This is the only category where I can say the original is undeniably superior. The soundtrack in TS isn't terrible, but a lot of the tracks just sound bland and those that do sound good are still sound inferior to the original tracks they replaced. There were only like 2 times where I thought TS's soundtrack was better.
Gameplay
Like with graphics, TS has much better gameplay mechanics which isn't a surprise since its based on MGS2 which was a natural progression from MGS1's gameplay. However, it does make TS too easy in some places. While, the original's mechanics are much more limited the game is still fun and is much more challenging. However, the original can also be much MUCH more frustrating.
In the end I think the question comes down to which element is more important to you, gameplay or story? If its gameplay then definitely TS. If story then the original if only because the better soundtrack gives the dramatic scenes more weight and the voice acting is more than good enough. Of course that is assuming the dated graphics and gameplay don't turn you off.