I've seen a lot of variety, really depends what you plan on doing and what kind of challenge you're after. Do you want to adhere to the game's main rules and focus on survival and dps? Do you just want to fish, or be a fish? Do you want to get the most out of flying, love teleports? What about cooking, parkour, pvp or pve, transmog, etc. All those things can result in a different answer of what suits you.
I've found mose nonconventional (usually not pvp) low levels do so for their own niche reasons, and they're a rare breed. That said, if you're looking at what can still function well in combat, that depends on how you play them and what trinkets you use, with a few exceptions.
Those exceptions are as follows:
Rogues, very weak in most cases, pick if you're looking for a challenge.
Mages, not as weak as Rogues but still a royal pain to solo.
Pally, sorry but low level pallies struggle unless put under the right conditions, namely having an advantage of some sort. They lack dps and survivability outside of their bubble, and even the DK has those.
Evoker, Evokers just lack the sustain in my experience. In a group they can bring the power, but their designed to offer support and it shows in their skillset when alone.
These are only my personal takes on them, mind you, and others will have their own opinions. Realistically, you can play anything, so long as you're persistent enough to work with its limitations.
