Most versatile class
There are several versatile classes, but it really depends on what you want to do. I understand you want a class that goes well in any game mode, but depending on what you want, the classes “Strength” may influence your decision to play it or not.
Such as a class maybe be versatile, but it excels in being built for Condition/Power Damage, or one may be better as providing Support/Heals and a few may be best suited for times where you need a “Tankier” or class that has good Damage Mitigation.
I can say, out of all the classes I have played, my Ranger and Guardian are my favorite classes, because they achieve what I need them to, while offering flexibility/versatility when and if I want to swap into a different role.
https://www.twitch.tv/amazinphelix
Ranger achieves that for me. It offers much with the pets, and bunker/tanky builds work, so does ranged glass cannon, or heals, Condi or power, full ranged or full melee, all can be played effectively imo on a ranger. I never get tired or bored of playing it because of the multiple ways I can play mine. They are good roamers, I pew pew pew ppl to death b4 they even reach me half the time in WvW, and I have good escapes when things get too hairy. They are great in PvE too of course, for raiding or fractaling or w/e, I have 0 troubles in those modes and even feel more useful than my teammates cause I can zoom around a battlefield/boss to rez or heal and buff with ease. They are very fast and mobile, with the exception of thief, every other class I play feels more slow and clunky in comparison.