Nollet and Collinson represent opposite ends of the scientific community spectrum, a spectrum that Franklin falls in the middle of. On the one hand, we have Collinson, who's English, friends with Franklin, and a member of the prestigious Royal Society. On the other, we've got Nollet, a snotty French scientist who openly disagrees with Franklin's ideas. Nollet lets emotion get in the way of reason when judging Franklin's work, while Collinson, in spite of or because of his friendship with Franklin, strongly defends it. Franklin himself contributes ideas, but doesn't engage in this active scientific debate: that's left to "experts" like Nollet, who attacks, and Collinson, who promotes. We don't think this contrast reveals any particular political statement about French versus English science; if anything, Franklin and his ideas have tons of French supporters. Instead, it shows the gap between kinds of science and approaches to invention, contrasting egotistical close-mindedness with open-minded progress.
In Franklin's religious development, he's impressed by encounters with two very different preachers. Hemphill and Whitefield make for a sharp contrast, and actually reveal as much about the kinds of people who make up their congregations as they do about themselves. Hemphill has good sermons, but they're not original, so he doesn't last long. Whitefield is a great speaker, but some people have problems with his doctrine. Neither one's the complete package, and each, in his own way, illustrates some of the problems Franklin sees with organized religion.