My experience in few words.
Remote Play using PS Vita and PS4 connected using LAN cable. At home
It takes second to start. The straming is awesome. It is so smooth that you could think you are playing a game on Vita. If you've tried it, you know what I mean. 9 out of 10
Remote Play using PS Vita and PS4 connected using Wifi connection. At home
It takes second to start. The straming is good, but here and there you have lag and noise. 7 out of 10
Remote Play using PS Vita and PS4 connected using LAN cable. Outside
It takes a minute to start. The straming is surprisly good, but here and there you have lag and noise. 7 out of 10
Remote Play using Nexus 5 rooted and PS4 connected using Wifi connection. At home
It takes ages to start. The straming is average, laggy and choppy. Not good enough to justify to play this way imo. For sure it depends on the wifi connection on PS4. 5 out of 10
Remote Play using Nexus 5 and PS4 connected using LAN cable. At home
I cannot make PS4 to recognize my Nexus 5. Dunno why. It could be great but I cannot check it out.