Each local area is going to be different so there is no real hard answer. All your answers are going to be via Google Searches for reviews of companies in your area, etc. Also asking around might help, but you'll get farther on Google, Facebook, etc. As for which "niche" is profitable, entirely up to the quality of service, solutions offered, how much it costs to buy, run, and maintain vs how much you charge (after payment processing fees are taking out). Also, little IT business struggle in any area if they are not constantly advertised, spread via viral content and word of mouth, etc.
So if you really are up for such a service, do some local google keyword research. If nothing really turns up, you'll still have to fight with the big boys like Geeksquad for sales. Even if you live in a fucking hill boon town in the mountains you will still need to do the basics. Advertise a quality product and or service, provide a unique customer experience along with excellent customer support, and invest your profits into multiple outside assets to shield against reliance on sales to generate money.
