Guild Wars 2

How does it work when using a shield when leveling? How does it work and what weapons are the best to have as main handed, and for swap? Is it even fun to play with a shield???

Shield can be good against some big enemy during the story (a boss or some undead army). I’ve leveled up with sword+shield, but just for fun.
That’s because in exploring you don’t need to preotect: you need to kill your enemy.
The best for exp is Axe/X (Mace can be good, for 10 Vulnerability and AoE knockdown, expecially in dungeon [axe skill 2 + mace skill 4 + on my mark = 24 stack of vulnerability]) or Greatsword for 100Blades and Whirl (and mobility to move around the map).
If you like to go a little ranged you can use a rifle or a longbow. Rifle for direct damage, longbow for condition and firefield (might), but in exp or World Boss I prefer Rifle (better direct damage).

I had fun with sword because of Bleed and condition damage, but to level fast a direct damage is better.

Try your weapons and play like you want. In that game you can level up fast, then chose the play style that make you like that class and play :-)

Efficient leveling is all about moving fast and killing fast. Shield does neither.

Greatsword brings both mobility and damage. Mainhand axe and offhand mace bring damage. Mainhand sword and offhand warhorn bring mobility.

Fun is subjective.

Shield with missile reflection works fine against the young karka in Southsun. That’s about it (and doesn’t help you to level).

I like using shield with mighty defenses trait for easy might stacks when taking on multiple foes. Turning a defensive weapon into an offensive augment is awesome. It helps set up skills like Eviscerate nicely. I play GS/axe/shield on my warrior and I thoroughly enjoy it (yes even for leveling). Sure, you could probably do a little more damage using a mace off-hand instead of a shield, but when you are a low level and busy leveling, the damage difference is hardly noteworthy. You kill things maybe .1 second slower with a shield than with a mace. Honestly, give it a try and keep playing it if you enjoy it like I do. If not, try a mace off-hand or anything else. The key thing is that you enjoy playing your character.

For pure leveling in open world PvE, I would recommend sword/warhorn + greatsword.

Savage Leap, Whirlwind Attack, Rush and Charge (swiftness) for maximum mobility. The idea is to move to the next spot quickly to gain more xp. You can always swap to axe/shield if there’s a heart or event that needs more to complete. Nothing says you have to use the same weapon set all the time in PvE. Rather, you should get use to swapping to different sets when the situation arises.

Ah, and once you get an elite, signet of rage will cover charge’s 5s downtime on swiftness.

I leveled up my first warrior with a/a and later swapped to a/shield when i realized Axe aa hits harder then most anything else.

I agree with the max mobility sentiment in open world pve.

Currently on my zerker open world pver I use s/a, gs. Still lots of raw dmg with final thrust and both offhand Axe skills.