Hey,
from that two, my bet goes on MGS1+ PS1. Plain and simple,
played both MGS1 and Goldeneye, and I think MGS1 will be more worth your time.
One more advantage is availability - it's hard to borrow a N64 game when so few people bought the N64 (although it had some great games) - you'll be forced to buy games, although they are cheap now. The PS1 is another story, I can count people with my fingers that havent got at least 3-4 PS1 games, so getting them cheaply/borrowing shouldn't be a problem.
However, when you mentioned N64, one game to my mind, and it's truly a great game - Conker's Bad Fury Day. If you havent played it yet, do yourself a favor, and play it! If you have an Xbox, get the revamped version (well, the only thing new is graphics)...
Conker is on my TOP10 list of games of all times, it has virtually no replay value, but I've played it 2 times, as it's just too damn funny, and I think it's a perfect game to relax yourself with during the Christmas break...
So, if you get Goldeneye, Zeldas AND Conker (the most important one), for 20 quid, forget PS1, and have the time of your life