One of the easiest teams IMO are the teams with a lead, a defensive core, and one or two revenge killers, AKA glue.
A lead is usually a very fast Pokemon that can scout what set the enemy is playing with, and usually carries moves like U-Turn and Volt Switch. A really common scout is Crobat, simply because he is so fast.
The defensive core usually consists of a water+fire+grass combination that can deal super effective or neutral damage to, aswell as counter, almost everything with diverse movesets and STAB moves.
The revenge killers are Pokemon with very diverse movesets and usually carry choice items and can therefore counter a lot of big threats to your team. And also, if one of your Pokemon dies, you can send a revenge killer in to sweep them away before they can kill any more team members. An extremely effective revenge killer would be Shadow Tag Chandelure, as he can learn lots of coverage moves like Psychic and Energy Ball