I lived on both islands during part of my residency. They are really different as you mentioned.
La Martinique is mostly welcoming to tourists, including Frenchmen.
La Guadeloupe on the other hand has a very ambivalent relationship with the Métropole (= the French State) and consequently with French tourists (The Independance movement is more developed there) ; hostility is more prevalent and can be off-putting. You clearly have to walk on egg shells when interacting with some people and they won't be shy expressing their displeasure at seeing 'foreigners' on their territory.