The two most useful changes you can make to a 1911 are the trigger and sights. The trigger must be manageable and the sights have to be visible. The tiny little G.I. sights I used as a young tank driver in the Cold War wouldn't work for me today as a gray-haired old coot with failing eyesight. I need larger sights with a wider notch in the rear and a large post up front I can focus on.
I often recommend Novak fixed sights for self-defense pistols because they are simple, low profile, well-made and tough. The only drawback to the Novak Lo-Mount rear sight is that the slide must be machined to accept it increasing the installation cost substantially.
Over the last couple years, I've been installing an increasing number of rear sights from Harrison Design out of Kennesaw, Ga. Their HD-003 Retro rear sight looks somewhat like a bloated G.I. model with nicely rounded corners and a wide notch. It is designed to fit the standard rear dovetail found on many older 1911 slides with fixed sights.
The rear face is serrated and there is a set screw hidden in the bottom of the notch, although retaining a rear sight with only a set screw is not something I would recommend.
The base of the HD is slightly oversized for proper fitting to the slide dovetail. The slide dovetail can be cleaned up with a 65-degree sight base file until the HD is a press fit. Tap it in place with a soft brass or aluminum drift.
According to drawings of the original 1911A1 G.I. sight, it was .245 inches high with a tiny .080-inch notch. The HD is .319 inches high with a .136-inch notch. The excellent Novak Wide Notch rear sights sport a .140-inch notch, and the HD could easily be opened up if necessary.
Although the HD is larger, it still has that "G.I." look to it and installation can be accomplished by the end user without a milling machine. It's higher than the original, but not excessively so and it is certainly low profile enough for everyday carry. Mate this rear sight to a .125- to .130-inch wide front sight .165 to .175 inches high and you should be good to go.
The Novak rear sight is nicely recessed to avoid glare and is available with tritium or fiber optic inserts or white dots and with notch sizes of .125, .140 or .170 inches. Harrison offers one model of the HD in basic black. Advantage: Novak.
Sending your slide to Novak to have their lo-mount rear sight installed can set you back more than $100 depending on which model you choose. The HD is $40 from Brownells, and you can install it yourself or have your local gunplumber do it for a minimal charge. Advantage: Harrison.
A Novak nicely melted into the slide certainly is sexy, but I think both sights look good. You'll have to decide which product best suits your needs and wallet. You can't lose either way.