Are there any real differences between factions in Ingress?

There isn't any difference, and there isn't any indication of this choice ever having an effect, gameplay-wise.

The only difference between the two teams is that The Resistance seems to be more popular, and will probably remain so in the foreseeable future. So if you desire a more challenging gameplay, pick the Enlightened.

Resistance as loners is not true in my area. The personality of the faction varies between regional areas (even varies between areas of cities). There is no difference in gameplay (both factions capture portals and try to link them to create fields). The only difference is in the storyline of the game (which you can ignore if you want). In the beginning, the Resistance was against alien influence of Earth's society. The Enlightened side with the Shapers who have influenced human society with the use of XM. The Resistance try to stop this influence. More recent story elements have added a second a second alien race the N'Zeer. The Resistance hopes to tap the N'Zeer's use of AI to continue their resistance against the Shapers. The Shapers were against the use of AI, so the Enlightened now also work to thwart the influence of N'Zeer AI. According this storyline, both the N'Zeer and The Shapers have influenced humanity. I guess the Resistance feels that AI is easier to control than XM influence; while the Enlightened fear that AI poses a Terminator type threat. Essentially, Niantic (makers of Ingress) have tried to make the storyline balanced so that both sides can be right/good guys and both sides can be wrong/bad guys. So really, I would suggest you choose your faction based on who you want to play with. Go to a big public park (it is probably a portal farm), find someone playing who you like (probably walking laps around the park staring at their phone the whole time), and join their side :)

Meta and gameplay wise no, story wise it's basically " do you want to help advance humanity through accepting alien help or by turning us all into robots"