Most Marth's on this concept = 
I'm here to clear it up.
Each Marth is different. He's such a versatile character and thus can be played in many different ways. But the most common thing you notice almost straight away when watching a Marth is this : Is the Marth aggressive or defensive?
"Hmm, looks like he is <insert playstyle>, is that right? Shouldn't he be doing it the other way.. isn't it more effective?"
Marth is about putting your opponent into traps with your sword while you stay at low risk. If you are a defensive Marth then you can do this.. in fact it's incredibly easy if you are defensive. If you are defensive you are using brick walls (SHDF, nairs, dtilts, etc) to keep your opponent out while you stay safe and punish his mistakes.
It sounds easy and it sounds very effective. It is. But like everything (besides metaghey), it has its weaknesses. For one, your opponent can control the pace of the match. Since you aren't really approaching, your opponent can decide when to strike. Let's take Sheik for example. You are SH retreating fairs to try and camp her, but it won't really do anything until she decides to approach you. She has so many options at this point, she can dash to shield, she can use her dart-like dash attack and punish the 5 or so frames of landing lag (i'm really unsure on the number) you have, she could roll behind you as you fair and grab you as you come down, or she could just throw needles at you. Different characters have different options, and as long as you are defensive those options expand and they will eventually find a way in.
This is where the aggressive Marth succeeds. His sword is always in the opponent's face and yet Marth is still in a safe position behind it. If you approach then you have effectively limited a LOT of your opponent's options compared to how many he had if the Marth was patient and defensive. Now YOU are controlling your opponent. You are putting him into auto-traps that are harder to get out of. It's pure sex.
But of course, with this many pros there must be many cons:
You have to be pinpoint in your approach. If you make one spacing mistake then your opponent will surely punish you for it. You must still focus on hitting with the tip to keep yourself safe.
You are constantly attacking. This means that you are basically committed to an action and once you do it you can't take it back. If your opponent uses a certain move that has priority or counters something that you will be unable to respond to it.
Perhaps you will just overexert yourself and put yourself in a bad position where you are left open.
Basically, all this means is that aggressive Marth is HIGH risk HIGH reward. It's much harder to execute compared with defensive Marth. If you choose the aggro route, know that you are taking the high road and it will require a lot more time and practice to make it work. Make a mistake and you will be left open and hit.
But do know that while these styles are very different, they still share some of the same qualities. Whether you are defensive or aggressive, you are still relying on zoning and pokes to rack up damage and keep yourself safe with your sword.
They are both very effective, in the end it really just depends on the player. There is no for sure better style, though if I had to choose then aggressive would probably come out on top.
tl;dr version:
Defensive Marth: Effective, Easy to do
Aggressive Marth: More effective and rewarding than defensive, Very hard to do
NOTEEEE: even though aggression is usually the way to go, sometimes you may have to turtle vs characters such as MK or various heavies
I'm here to clear it up.
Each Marth is different. He's such a versatile character and thus can be played in many different ways. But the most common thing you notice almost straight away when watching a Marth is this : Is the Marth aggressive or defensive?
"Hmm, looks like he is <insert playstyle>, is that right? Shouldn't he be doing it the other way.. isn't it more effective?"
Marth is about putting your opponent into traps with your sword while you stay at low risk. If you are a defensive Marth then you can do this.. in fact it's incredibly easy if you are defensive. If you are defensive you are using brick walls (SHDF, nairs, dtilts, etc) to keep your opponent out while you stay safe and punish his mistakes.
It sounds easy and it sounds very effective. It is. But like everything (besides metaghey), it has its weaknesses. For one, your opponent can control the pace of the match. Since you aren't really approaching, your opponent can decide when to strike. Let's take Sheik for example. You are SH retreating fairs to try and camp her, but it won't really do anything until she decides to approach you. She has so many options at this point, she can dash to shield, she can use her dart-like dash attack and punish the 5 or so frames of landing lag (i'm really unsure on the number) you have, she could roll behind you as you fair and grab you as you come down, or she could just throw needles at you. Different characters have different options, and as long as you are defensive those options expand and they will eventually find a way in.
This is where the aggressive Marth succeeds. His sword is always in the opponent's face and yet Marth is still in a safe position behind it. If you approach then you have effectively limited a LOT of your opponent's options compared to how many he had if the Marth was patient and defensive. Now YOU are controlling your opponent. You are putting him into auto-traps that are harder to get out of. It's pure sex.
But of course, with this many pros there must be many cons:
You have to be pinpoint in your approach. If you make one spacing mistake then your opponent will surely punish you for it. You must still focus on hitting with the tip to keep yourself safe.
You are constantly attacking. This means that you are basically committed to an action and once you do it you can't take it back. If your opponent uses a certain move that has priority or counters something that you will be unable to respond to it.
Perhaps you will just overexert yourself and put yourself in a bad position where you are left open.
Basically, all this means is that aggressive Marth is HIGH risk HIGH reward. It's much harder to execute compared with defensive Marth. If you choose the aggro route, know that you are taking the high road and it will require a lot more time and practice to make it work. Make a mistake and you will be left open and hit.
But do know that while these styles are very different, they still share some of the same qualities. Whether you are defensive or aggressive, you are still relying on zoning and pokes to rack up damage and keep yourself safe with your sword.
They are both very effective, in the end it really just depends on the player. There is no for sure better style, though if I had to choose then aggressive would probably come out on top.
tl;dr version:
Defensive Marth: Effective, Easy to do
Aggressive Marth: More effective and rewarding than defensive, Very hard to do
NOTEEEE: even though aggression is usually the way to go, sometimes you may have to turtle vs characters such as MK or various heavies
Its all about agression baby 
