I have a quick question. Is will o wisp a far more useful move competitively compared to fake out on a new moveset?
There is no clear answer to your question.
Both of these moves are useful in their own right and the choice actually depends on the Pokémon in question, as well as the role that this Pokémon is supposed to fulfil on your specific team.
The only Pokémon that can run both of these moves at the same time are Mew, Smeargle, Sableye, the Chimchar line, the Litten line and the Salandit line.
When it comes to the aforementioned Pokémon, Mew and Sableye are the only Pokémon that make use of Will-O-Wisp.
While some Sableye, specifically Mega-Sableye, movesets run both of these moves, Mew only runs Fake Out in the Doubles OU format.
The Chimchar line and the Litten line make use of Fake Out for example, the former as a way to function as an anti-lead Pokémon that can break a Focus Sash or an opposing Pokémon's Sturdy ability and the latter in the VGC Doubles formats to flinch a Pokémon to prevent it from doing something. These Pokémon do not run Will-O-Wisp because they mainly focus on dishing out damage and pivoting around with U-turn.
The Salandit line, despite having access to both of these moves, never uses any of them. Salazzle's role is to boost its Special Attack stat and to dish out heavy damage quickly before an opposing Pokémon can knock it out easily because of its frail nature. In this case, having these moves would not benefit the role that Salazzle fulfils.
Last but not least, while Smeargle can sketch both of these moves, they are not really all that helpful and Smeargle prefers running Spore and entry hazards like Sticky Web, Stealth Rock etc.
Ultimately, it all depends on what your teams needs.
If you feel unsure, feel free to look up movesets of the respective Pokémon in
Smogon's Strategy Dex.
There you can find peer reviewed analyses that will tell you exactly what each move is supposed to do and how to use the Pokémon to the maximum of its capacities.