Being a relative beginner (only 1 1/2 years quilting), it is important to pick a block that is equivalent to your skill level. If the block is too hard, you may become discouraged and may not complete the quilt. If you are the kind of person who really likes a challenge, that is probably not aoing to be an issue.
To me, though, it is important that I really ENJOY the process of putting the quilt together. So, I carefully look at blocks and think long and hard before picking something. I want putting the quilt together to be FUN! Squares and rectangles are easy, triangles can be troublesome. I do include some triangles even so and don't mind ripping them out if they don't come out just right.
Just my opinion......