Versatility?
You’ll need to build to compensate for the low health pool (lowest in the game on guard) but with a bit of vitality and a good boon uptime a guardian is one of the most, if not the most survivable character in game.
Guards are not squishy at all, but it does require some more active self support. If done correctly you are more tankier then most without having to sacrifice not much dps.
Warriors are dps monsters. They are easy to play, purely based on dps and are basically “press 1 to win”. Allthough: DPS = verstality, I find it a boring class.
Keep in mind that in PvP builds are often switched. Gear is for free in sPvP and changing skills and traits is for free (and all are unlocked at level 2). So most people use a specialised sPvP build.
I also believe strongly in a separate build for WvW. It takes not much time to set it up (and cause I prefer playing ele there myself, I just got a dedicated WvW ele, just cause I’m lazy and don’t want to switch). The reason is that there is only one succesfull buildtype for PvE, while that is not optimal for WvW.
PvE build is zerker. The reason is very simple. The game doesn’t tanks or healers. although DoT is good, manipulating it through gear is a bad move cause of the way the DoT cap works. So it is a matter of staying alive and dealing max dps. As you can stay alive in all circumstances with a zerkerbuild and cause that deals the most dps, that is the way to go in PvE.
In WvW it depends a lot more on your class, the role you play and the place in the zerk you take. Even race is a factor here (imagine two warriors. One is a charr, the other is an Asura. Due to the size, the charr will likely get more agro from the other zerk and so it is more beneficial to act as a tank-like char® for your zerk. While the Asura is easier ignored due to the small size and is more suited for dps.)
Arise, opressed of Tyria!