Whatever grip you are strongest with should be your competition grip. While some people say you should use the widest grip possible, some of the best bench pressers (James Strickland and Jeremy Hoornstra for example) use a relatively close grip so there isn’t one way that is best for everyone. Wide grip bench is a good assistance exercise, some well known coaches like Louie Simmons and Josh Bryant use them with their lifters. Josh Bryant says not to go below 6 reps on them because the wide grip puts more strain on your shoulders and pec tendon that will increase the risk of injury, and also do them with a pause to train the initial drive off your chest.
If you are going to bench with a close grip then make sure to build up your triceps, they will be a limiting factor. Close (closer) grip variations, dips, tricep extensions, JM presses, etc.
For me its as simple as the grip width that means my forearms are perpendicular to the floor when tbe bar is touching my chest. This will be different widths depending on where you touch the bar, above or below the nipple, and obviosuly on your own relative lever lengths.
But vertical forearms has always been the sweet spot for me.
I agree with Chris, do what’s comfortable. Work your triceps very hard. Also do alot of back and rear delt work, some chest. I use the wide grip benches on my 2nd Bench day. It really works the pecs hard
The narrower you go (within reason) the stronger you will be (up to a point).
Whether you are better off moving the bar a shorter distance in a weaker position or moving the bar further in a strong position is really, really individual. You’ll need to work it out for yourself.
It is a similar case for how low on your body you touch the bar.
To add to this, what grip width you are strongest with will also depend on which muscles are strongest. Wide grip = pecs and shoulders, close grip = triceps.