Given the choice between a Trijicon SA39-C-600716 sight and a TruGlo TFX Pro sight for a Shield 9 mm, which would you choose? Why? Other suggestion?
I actually have both. I have the TFOs on my M&P 45 and the Trijicon on my 1911.
The TFOs are great sights in really bright light. They work well in very low light conditions. In dusky conditions they're just OK. In bright light the fiber optic rods really pick up the light and they glow very brightly. In really low light they have tritium in them and glow bright enough. In dusk level light, there isn't enough to make the fiber glow and it's too light for the tritium to work well.
When new, the Trijicon sights are fantastic. The white ring is very clear in daylight. At night, even during dusk, the tritium glows enough to be easily seen. However, as they age, they don't hold this ability. The white has completely worn off of my front sight. So, during the day the sight is basically just black now. That happened fairly quickly. The soot from the muzzle just makes it dirty and the white gets obliterated. Now, I've shot this gun a lot and have right at 10k rounds through it. Also, the sights are now about 13 years old and the tritium doesn't glow any more. Still, it's a good sight.
But you asked for other recommendations. Honestly, I like the stock sights a that come with M&P guns. The dots are bright enough to be easily seen during the day. If the lighting is so dim that you can't see the dots, can you really positively identify your target? Also, the stock sights have a ledge on the rear sight which makes it easier to rack the gun with one hand. This won't be a common issue, but it is a nice feature to have.
In the end, that's my opinion. You're already a pretty good shot and your target is better than most. The stock sights will serve you fine. A red dot might help more, but that's another discussion.