I use a regular disposable fixed-head two-blade razer. I do it in the shower, and use the lather from my shampoo as shaving cream. You gotta use the off hand to stretch the skin flat so you dont have any ridges to catch, and shave in a direction that you never feel any snags starting (for me it's usually going from the center outwards,and slightly upwards).

I have tried various trimmers and never found one that could get a close shave without getting cuts. I also tried an epilator (a device that rips out hair en masse. Bought one made for girls because some reviews said its gentler). That works well for everything but the sack. Tried a couple different razers, but found that ones with too many blades dont navigate the tight spaces well, and ones with flexible heads dont give enough control to respond to the curves and very directional hair.

No matter what, you can't shave down there with the same "machete in the jungle" approach that can work for a beard. It's a more precise process, and requires a bit of practice to get good at. That said, I've been happy with my routine now that I've got it figured out.