Oh, man, this is a tough one. If we're talking straight-up character versus character, I'm going to have to give it to Link.
While Marth possesses the fluidity, speed, and technical potential that separate himself and Link on most tier lists, Link simply has more defensive and approaching options at his disposal. He can use bombs to dole out heavy damage from afar, use his arrows to keep Marth off of the stage (whose recovery happens to be mostly horizontal in the form of his forward special slashes), and use the ever-useful Boomerang to approach, pressure, and combo.
This is where the matchup gets really tricky for me to decide. Marth and Link have very comparable ranges between Falchion and the Master Sword, but Link simply hits harder in most cases. This comes with higher end lag on most of his moves, however. Marth, on the other hand, can hit faster, but can only really match Link in straight up force when spaced properly; something which is difficult for a player who plays Marth for the very first time to do (I would assume).
Link's grab, in the form of the Clawshot, is an incredible tool in terms of grabbing reach, and aerial combo potential. It deals a nice amount of damage in the air, aids in Link's otherwise-poor recovery (with the help of the Bomb Jump, as well), and is an excellent option out of shield. Marth, while having an incredible reach for his grab, cannot use it as a recovery, or a ranged aerial attack like Link can. Though, if Link misses with the Clawshot, he can be punished very easily.
You know, I actually can't decide on this one. Once Marth closes in, it seems to be his game. Link's vast array of tools are very difficult to use up close; bombs take too long to ready and throw, and can end up hurting Link as well. The bow suffers from a long charge and startup, and the Boomerang, well, it's still relatively handy. Link's main advantage up close with Marth, is that Link doesn't require any advanced spacing to deal the kind of damage he does. I would like to think that even though I can combo relatively well with Link, that a Marth player who knows how to utilize his full potential would walk all over me, even with Link's distinct ranged advantage.
In terms of pure technical ability, I'd give it to Marth. A player who knows what they're doing with him would probably be able to outmaneuver a Link player, even at a higher level like Hylain's. Though, at the same time, a skilled Link can zone with the Boomerang, and give Marth a Hell of a time trying to close in.
I really can't choose.
VS 
