I've played both mods for long periods of time, so I think I can help here.
Hidden is easier for most players to adjust to, and is generally much more popular. Unlike in many games, hidden increases the area covered as your combo increases, however, it maxes out about halfway up the screen at 500 combo, leaving the upper half of the screen visible. This means that even at 500+ combo it's perfectly playable. In fact, I played better when the hidden region was near or at max size.
The benefit of vision mods like hidden and flashlight is mostly that it reduces the amount of notes on the screen at once. This can make it easier to read the patterns before you have to play them. It also forces you to pay more attention to the music for your timing, instead of watching the notes reach the judgement line.
Flashlight is much more difficult to adjust to than hidden, and requires you to use a slow scroll speed in order to be playable. For example, before I switched to playing full time flashlight, I was playing with hidden, and my scroll speed was about 27 fixed. When I switched to Flashlight, I lowered my scroll speed to 13 fixed. Flashlight forces you to use the music for timing much more than hidden as well. Another issue with flashlight is that since you are forced to use lower scroll speeds, the patterns are much denser, which can make it harder to tell the exact timing of certain notes.
The reason I switched from hidden to flashlight is because FL actually helped me read difficult patterns with more LNs better than hidden did.
Personally, I suggest most players stick to using hidden, unless you want to commit to using flashlight 100% of the time. After I started playing flashlight for several months, I tried playing with hidden or no vision mod, and found out that I can't. At all. I've completely lost the ability to play without flashlight now.