Easiest and best martial arts?

I have a third dan black belt in shotokan karate.Its really good but not exactly easy.Stamina is needed.Gradings for the coloured belts are every 3 months except the final brown (there are 3 brown belts) which is 6 months.

I used to take my little brother to tae kwon do classes. They were easy enough for him to follow along and remember the moves. Not sure about many others. I think every one of them starts off fairly simple for beginners.

Krav Maga

None of them are “easy” it takes actual work and commitment

What form interests you more? I enjoy grappling so I wrestled and do BJJ.

It depends what you want. If it's physical fitness, any of them will work. If it's self defense, Krav Maga is a good choice as it's designed to neutralize the enemy as fast as possible.

The Asian martial arts can be very effective, but are based more on developing mental discipline through precision movements. So if that's what you're after, Tai Chi is perfect for that because it is the moves without the fighting.

Never karate, Wing Chun, Krav Maga, Jeet Kune Do, Brazilian Jujitsu, and Kung Fu are good.

Brazilian Capoeira is very difficult but extremely effective.

Muy Tai also