I should probably point out that a good Link can definitely out camp Pikachu. I faced a great Link in tournament at Battlefield and lost because I couldn't get near him. My advice would be to not get into a camping war with him because you will have a lot of damage before you know it. I'll just run through Link's moveset. I actually picked him up recently for fun and was surprised by how good he can be.
Jab: Link has a three-hit jab that he can cancel just like Ike can. It is one of his fastest moves and will be used often to get you away from him.
Dash attack: There's nothing too special about Link's dash attack. It has average knockback and average speed. You should be able to shield grab it, but I doubt it's slow enough to punish with much else.
Aerials:
Fair: A slow but fairly powerful attack. Most Links won't use this move much due to its lag. Unless you are careless, you shouldn't get hit by this move.
Dair: One of Link's killing moves. Though it may seem obvious that it's coming, it can actually sneak up on you if you are too concentrated on juggling. It also can poke through your shield so the best thing to do is to get completely out of its way.
Bair: This move has the second least startup lag of any of Link's aerials. If the first and second kick hit you, you will go backwards. If only the second kick hits you, you will go diagonal. Don't be surprised if Link uses this as a pseudo wall of pain in battle. Links also find reverse aerial rushing especially important to their game, so watch out.
Uair: This move can't kill you as well as dair, but it still can kill you all the same. It has a lot of lag, so be sure to punish Link for missing it.
Nair: This is Link's sex kick. It is his fastest aerial, and he will use it to try and break out of Pika's awesome aerial combos.
Smashes:
Fsmash: It's a two hit move, though you can usually avoid getting hit by both by shielding or DI-ing. It is one of Link's better kill moves. He can just hit with the first part and kill you. If you want to stay on the safe side, you can just tjolt Link when he does this. Personally, I would use the opportunity to set up a combo with FF fair.
Usmash: It's one of Link's best juggling moves. It is multi-hit, so make sure you land away from it. Don't try to outprioritize it with dair because you will get punished. Usmash can kill you, but it is usually not used for that. If Link uses his dacus when you are on the ground, then just shield the usmash and punish him with a grab combo.
Dsmash: A slow killing move. It hits both sides. Take advantage of the huge lag on this to punish him. Most of the time, this move will not hit you unless you are careless.
Tilts:
Dtilt: This move can spike you on the ledge, but it is very slow and you are very fast. It's more likely that Link will try to edge guard you with projectiles than dtilt.
Ftilt: If you are approaching from the ground, Link may punish your aggression with this slow but high priority spacing move. It's one of Link's many gtfo moves and can kill Pikachu at high percents.
Utilt: Good for juggling just like usmash. It has a wide range and won't hit you very far, which means it will be strung together with Link's few other comboing moves.
Specials:
Neutral B: Arrows are a relatively safe move for Link because of their speed, but you can punish them if you are close and approach him from above.
Down B: Link's bomb is good if he is camping you, but you can pressure him to use it early if you "approach." Just pretend to approach and shield and he will get rid of that bomb very fast. He will try to use it to control the stage and just plain spam. Don't get hit with bombs at high percents, or you could die.
Forward B: Gale boomerang can be fun in my opinion. Link will use it to get you away from him so he can camp some more. He will also use it to try and edgeguard you (it's not very effective). Be careful with this, but I like to ride on his boomerang and do an aerial at him. Just don't get smashed.
Up B: Ahh, this is Link's terrible recovery. It has high priority, but it doesn't get Link very far. Use a wall of thunder when Link is recovering or tjolt him and he will not get back. Link may try to use this on the ground. It is slow on the ground and can be shielded. The cool down lag is also very slow, so you should get a free hit.
Grabs:
Link's grab is terrible anyway, but here's what he can do if he does manage to grab you. Don't hesitate to punish him if he does miss his grab.
Fthrow: Not a very good throw for Link. He will kick you forward and it will give about 7%. He probably won't use this because it's hard to combo from.
Dthrow: Link will slam you on the ground and it will send you almost directly upwards. He will then try to combo you into an utilt or possibly a bair.
Bthrow: Throws you directly backwards. Links will use this often for spacing.
Uthrow: This throws you directly upwards. It's not very useful for Link unless he throws a bomb up first and throws you into it.
Zair: This is Link's longest non-projectile attack. He'll use it to approach and possibly combo because the knockback is so little and it comes out fast. The chain also serves as a tether, which has OK range that sets Link up to be edgehogged if he misses.
Pikachu's Chaingrab: Pikachu can chaingrab Link to about 40% with the forward throw and about 55% with the down throw. Even though dthrow does more, it is more beneficial to use fthrow and get Link off the stage where he will have trouble recovering.
SUMMARY:
60:40 for Pikachu
Pikachu has the advantage here because of his chaingrab and overall speed. Link can still win this matchup if he can out camp Pikachu, but he is dead if he gets knocked off the stage. Pikachu's should not be too aggressive in this match unless they want to get punished with strong but slow moves. This matchup is good for Pikachu, just be careful.