I've used them at the youth and MS level for years. I like them because it cuts down on what the program has to keep up with. Every once in a while you'll have a pad invert or a belt pull up into a seam but IMO I'll use them at this level for sure.
Our latest pair of game pants has the knee pads in the pants---but there's a pocket so they can be taken out and replaced. I like them being there....just have to make sure nothing gets lost in the wash.
I just did it with our 7-JV programs and it was a blessing. Kids go from having to keep up with 5 items (practice pants, game pants, knee pads, girdles, and belts) down to 1 item. Parent loved it to. We got white under armour integrated pants and they were pretty thin. If you get integrated game pants for varsity, I think any color but white would look good.