To tell you the truth, I don’t really know how to answer this question. I’d suggest contacting and discerning with both if you’re considering a Franciscan vocation. But I’ll try to explain to the best I can anyway. I’ll also mention the important footnotes which have affected Capuchins.
There are historical differences, and this certainly affects the culture of the OFM Caps today. But Franciscan history is a bit complex and there’s a lot of misinformation. (For example, OFMs are NOT the oldest branch of the Franciscans despite what many think). In those days, there were two main groups of the Franciscans…1) Conventuals and 2) Observants. Anyway, the Capuchins were a reform movement in the 1500’s, that distinguished itself from “mainline” Observant Franciscanism. Their original goal wasn’t to break away, but to live a Franciscan life more aligned to the roots of Franciscanism…to live more faithfully to the Rule…really just more ascetical. They adopted a new habit because they thought it was closer to what Saint Francis used. They were also more interested in living contemplative lives (this is an important footnote). But some of the observant leadership didn’t like them, and the early reformers were persecuted for it. Some ended up taking refuge with the Camaldolese monk (another important footnote). This added to the contemplative nature of the Capuchins, and also our tradition says that this is where the characteristic long pointed hoods and beards Capuchins are known for come from. Then a plague broke out, during which the Capuchins realized they couldn’t live strictly contemplative lives anymore. So, they left the monastery and ministered to the sick and dying plague victims (another important footnote). The Capuchins were almost suppressed due to the Observants lobby against them, but a royal duchess witnessed the ministry’s of the Capuchins to the plague victims and became quite fond of the Capuchins. She was able to convince her uncle, the Pope, to protect the Capuchins, and the the order essentially took off from there.
What are the differences between modern OFMs and modern Capuchins? The habit is different. Some traditions are different, like the beard. But it’s no longer required for capuchins to have a beard anyway. At the end of the day, there really isn’t a lot of difference right now. Some of the OFM friaries I visited seemed to be fancier than most of the Capuchin ones, but this isn’t universally true. Capuchin friaries still tend to be in poorer areas, part of our history connected to the plague victims of old…going where we are most needed, and often that’s because nobody else will go there. That includes remote villages on remote islands in mission areas or South America, Africa, and pacific islands. Lay Brothers also tend to play a more prominent role among the Capuchins than among OFMs.
Honestly, there isn’t a lot of difference. There can sometimes be a greater difference between two Capuchin Provinces than between certain Capuchin and OFM provinces. The charisms, constitutions, and ministries are too similar, so for discernment, the best thing to do is to just spend time with them.