Honestly both are great, just different experiences.

Wildlands is arguably a lot more fleshed out. The story feels a lot more cohesive, the gameplay is very solid, the sniping is much better (the draw distance for enemies in Breakpoint is a lot lower making long range shots impossible). Wildlands also has an awesome first person mod on PC, makes it feel like one of the OG ghost recon games.

Breakpoint has a lot more survival elements. Large injuries make you limp, you can hide in the mud, craft medkits and stamina shots, etc. You're also alone on an island and basically everyone is an enemy. Really feels like you're behind enemy lines.

Wildlands is better for experimenting and fooling around, Breakpoint is better for getting immersed and intense gameplay. Just my 2 cents.