This topic has been done before! My previous comments and views were as follows
Firstly 355N is quite different from 355F; significantly more power, faster (130kts low skids no floats), much better Class 1 performance, much more reliable (engines), very quick to start and go, 1 min shutdown v 2 mins on the Fs.
Advantages 355N are mainly much better range than 135 (3 hours endurance v 2.30) , better ride comfort (135 is more fidgety esp in turbulence), better pax seat comfort and view, pilot/pax communication, ability to pick up/drop rear pax through big pilot door rotors running safely, lower price and hence insurance costs.
Advantages 135 are lower operational costs and downtime from maintenance, speed (probably 7 kts faster spec for spec), Cat A performance, baggage space, cabin volume, quieter outside, better quality avionics, generally more solid, more modern systems, better crash-worthiness.
Both excellent, popular aircraft with different role strengths.