The most famous American poet of his age and a Harvard professor of modern languages; his 1867 Divine Comedy was the first complete American translation and remains a faithful public-domain standard.
The faithful poet’s version, and free. Longfellow abandons rhyme for unrhymed lines that follow Dante almost word for word, so as a crib to the Italian it is remarkably close, and there is real dignity in the cadence. It is also of its century: the diction is elevated and inverted (“Midway upon the journey of our life”), and modern readers feel the age of it. His notes, drawing on a circle of Boston Dante scholars, are still worth reading. Come to Longfellow for accuracy and gravity at no cost, not for a contemporary voice.
Longfellow follows the Italian almost line for line and declines to rhyme, which is why it still reads as the most faithful free version in English. The diction is of its century and the word order sometimes bends to keep the line, but very little is added and very little is lost. If you want to know what Dante wrote rather than what an English poet made of it, start here. Free and complete.
The same method as his Purgatorio, and it pays off hardest here. Where the Italian is abstract Longfellow stays abstract rather than smoothing it into something easier, so the difficulty you feel is Dante’s difficulty. His Piccarda line, “his will is our peace”, is the plainest rendering of that famous half-line in English. Free and complete.