Choosing a GPU

You need to make sure to have as much memory as possible. Otherwise you simply can't train your models effectively (insufficient batch size). So, optimize for that rather than sheer performance.

A good old NVIDIA 1080TI (11 GB card) is still a good choice. If you can get the 2080RTX TI and it fits your budget, go for it.

Here's a guide quite helpful on choosing GPUs for Deep Learning.