I walked from St Jean Pied De Port to Burgous last July on the French Route with my wife, then returned in August and walked from Irun to Ribedesalla on the Northern route in August on my own.
I enjoyed them both but for different reasons. The French route was better serviced with Auberges, coffee stops and facilities. It was also much busier and had a greater variety of fellow walkers. It was my first Camino and I just loved it. The Northern route I found to be more difficult in comparrison. A lot more climbing and for the first stage as far as Santander an awful lot of asphalt. Having said that the scenery was spectacular, there is something about a view of the sea while walking that most people really appreciate. The same sea was of course very refreshing on many occassions. I met no native English speakers on the North route but this was not a problem as almost everyone (Spanish pilgrims included) speaks at least a little English, but this fact did embarrass me enough for me to take up Spanish classes for my return. I think that if you are speaking to a Spanish person in Spain you should at least attempt their language.
Basically though the fellow walkers/pilgrims that I met on both routes were some of the nicest people that I have ever met, and I have made friends with people from all corners of the world, for life I hope.
Back to your post. Based on what I know now, if I was you I would do the French route, particulary if it is in April for the following reasons; The route is easier to follow, I used the
John Brierley book and found it excellent, there will be more people/pilgrims on it at that time of the year, accomodation will be easier, at least 50% of the Auberges that I stayed in on the North only open in the summer months, the weather will be better on the French route, walking and swimming in the sea was great on the North but I doubt if it will be warm enough in April for that.
Whichever route you decide I am sure that you will enjoy either, you can after all return and do any of the other routes at any time in the future. I intend to complete the North route at end of March/April next year and hopefully return in July to complete the French route, this probably goes against my advice above but is purely driven by time available and my fellow companions and to be honest it's not really about reaching Santiago for me but more about the whole experience along the way. After about one weeks walking I think that you will understand what I am saying and I wish you well.