I'm 5'6.5" tall, stocky build, and about twenty pounds overweight. I use packers from 3.5" to 4".
I have a couple of Mango 3.5" gel packers; they're a pretty good size.
I also have a 4" Good Vibes packer with the firm core. Because it is firmer and slightly larger than the Mango, the GV packer is on the large size. But it's the smallest they had. I feel just a little self-conscious about it, but I like the texture so much that it's my regular pantstuffer.
I used to have a 5" gel packer. The balls were too flat, and the penis part was simply huge. I put it in my Tranzwear pouch for five minutes, looked at myself in the mirror, and had nightmares for weeks (okay, just kidding about the nightmares, but it looked and felt all wrong). I gave that packer to a friend of mine who is six feet tall and bulky. He seems happy with it.