I have a couple of different mindsets on line building with Nylander. I agree with a lot of what people here are saying, that JT is a bit too slow, and Holmberg was a terrible decision, as he really doesn't have NHL offensive upside. Patches was better, but again slow, though he had puck digging abilities.
Holmberg - JT - Nylander... 2 goals for 4 against.
Patches - JT - Nylander 6 goals for 2 against
Both lines were terrible in possession though, so it's possible with a great sample set, that it wouldn't have worked out well for either line.
On the flip side McMann - JT - Nylander had good possession stats... 1 goal for, 1 against. McMann can play physical, work the boards, and has some speed.
If we are lucky enough to do a sign and trade with Vegas... Marner for Karlsson... I think Karlsson makes a much better C for Nylander than JT. McMann - Karlsson - Nylander gives a very speedy line... Karlsson is 83rd percentile, McMann is 95th and Nylander is 68th... though his ability to move and control the puck is incredible. This is a pretty balanced, and fast line.
On the other hand, a guy like Ehlers is 94th percentile in speed, and him instead of McMann gives a ton of talent on one line... though it's a bit soft.
Given my preference is balance... I'd probably go with McMann - Karlsson - Nylander as a second line.
Knies - Matthews - Ehlers would probably make a good first line.