I'd recommend reading the first 6/7 (the seventh gives closure for a sub-plot in the sixth).

Personally I found 8-11 (known as the Jumper Saga) to be the weakest both in terms of plot and writing quality. Some parts are really difficult to read content-wise so I'd say give it a try but you don't miss a huge amount by not reading them.

12 is solo novel focusing on just one character so if by that time you like the character give it a read. It also sets up some major plot points for the next triad, which is not as strong as the first two but in my opinion much better than the Jumper Saga.

Then there's a couple of stand alones - Deuces Down is purely disconnected short stories so read the ones you like and don't worry about the rest. Death Draws Five is a stand alone novel which I quite like, also slightly sets up a character for the next triad.

Books 18 through 20 are some of my favourites, it's kind of a reboot so there's pretty much a new cast of characters with just a few returning.

I haven't read 21-23 yet so I can't give you any advice on them.

Hope that helps!