What will be _____'s best department in the first French election round?

[Tirnam]

Macron: Paris
Le Pen: Aisne
Mélenchon: Seine-Saint-Denis
Fillon: Vendée
Hamon: Paris

With overseas territories that could change. Fillon should have great score in Saint-Martin/Saint-Barthélémy, in Nouvelle-Calédonie.
Le Pen could have some success in Mayotte, French Polynesia, ...
Mélenchon maybe in La Réunion (he is endorsed by the powerful local Communist Party, even if they had a serious defeat in the 2015 local election)
Hard to guess who is going to win French Guyana with the serious crisis underway there.

[Tirnam]

Le Pen could have some success in Mayotte, French Polynesia, ...

I know very little about French politics but I don't understand why Le Pen would be popular in areas far removed from the EU and immigration.

Well Mayotte is facing a strong immigration pressure from the Comoros (Same in Guyana from Brazil, Haiti, Suriname, ...) and they have a feeling that the State has abandoned them (for example they had a great water shortage a few weeks ago).
In French Polynesia, Le Pen received some local supports, she had 20 signatures from there against 4 in 2012.