How many $$ you want to spend and what appeals to you. Before I knew it, I had a variety of straights razors with different grinds, shapes, sizes, and different steel and I easily became efficient with all of them.

The 1/2 is fun because it manuevers everwhere so easily.
The 5/8 seemed small after I use my 7/8. The 7/8 seemed big at first, but I manage to fit it everwhere the 1/2 goes.

Square points are handy shaving tight areas. Less intimdating than they look. Round point, more safety than I need.

The wedge makes less noise when I shave and I feel a bit retro using it.

You will likely get more than one straight razor, so don't let it weigh too heavy on your first buy. You will likely have others.

Pabster