As I have been playing D&D a lot more as a player (as opposed to as DM) lately, I have been looking at other people's ideas on what classes and sub-classes are especially good in D&D. And I quickly noticed that they all tend to disagree with each other. After thinking a bit more about the matter, I realized why this is so, beyond the obvious differences in personal preferences. Basically the style of your DM determines what the best classes for your game are.

Take for example this YouTube video of D&D class ranking: It is heavily skewed towards ranking spellcasters highly, and classes that can't cast spells badly. I looked at the video, compared it to what kind of character I would need for our RPG club's multi-DM campaign, and realized that this was exactly the wrong choice for that campaign. The average level of characters in that campaign is around 6. And the rule is that each session is one day long, long rests are impossible during a session, and for short rests you need to make rolls for random encounters. The result of those rules is that the "adventuring day" (as D&D officially calls it in the Dungeon Master's Guide) is long, often reaching the "6 to 8 medium to hard encounters per day" recommended. If you are a 6th level wizard, and you have 10 spells per day, it means you can cast only 1 or 2 spells per encounter, and then you are reduced to casting cantrips that do comparatively little damage. If you played that same 6th level wizard in a campaign in which the DM lets you take a long rest whenever you want (and often it isn't easy in a regular campaign to come up with a reason why the group wouldn't be able to take a rest), he would be a lot more powerful.

I was thinking what kind of spellcaster I would play in our "long adventuring day" campaign, and it would probably be something like the DFC Ultimate Healer, because healing becomes a lot more useful in such a campaign. But in a campaign with lots of opportunities for short and long rests, a healer is much less important. There is no penalty in D&D for being low in hit points, so if you can rest when everybody's hit points are low, the healer is only needed occasionally in combat when somebody drops to 0 and needs to be revived quickly. If you can't rest, healing spells between combat encounters become a lot more important.

So, what is the best character build for you game? It is a question impossible to answer without knowing how your DM runs the game. If you can expend limited resources like spell slots without having to worry about resource management and how to get them back, characters relying on such resources (e.g. spellcasters) become very powerful. If you DM is playing up the resource management, characters with higher base damage and less burst damage become more useful. I have a suspicion that multiclass characters are more powerful than single-class characters, because you can "break" things in the game by combining abilities from multiple classes (e.g. life cleric + druid for extremely powerful Goodberries). But other than that you really need to know the style of your DM, and possibly the classes of your fellow players, to really make an optimal build.