I chose 135 because it is 10 pounds into my healthy weight category. But to be honest, I'm pretty happy where I am!! I want to get to 145 for sure just because I'm stubborn and want to see "normal" on that BMI chart, but those charts aren't the end-all be-all. I judge more by size and I'm pretty happy wearing a size 8 after all these years.
I suggest getting to your goal of 153 (according to your sidebar) and seeing what you think. If you're comfortable there, great.
Goal weights are very subjective. They bug me sometimes too. I see a lot of women with goals far below mine and yet there are days I'm content to stay right where I am!