To do that question proper justice I would need a degree in textile science from MIT. Since that's not going to happen, here's my opinion: All four jackets you mention are waterproof, breathable, and so finely constructed that you'll last outside in a rainstorm for hours. All have a polyurethane coating, but they differ slightly in how they're treated. Marmot's Precip's ($100; marmot.com) polyurethane coating is impregnated with silicon dioxide particles that allow sweaty vapor molecules to escape, while at the same time don't allow big rain drops in. Mountain Hardwear's Epic ($120; mountainhardwear.com) has a polyurethane coating that contains silk proteins that give the inner fabric a softer feel next to your skin. And both the Isis Torrent ($129; isisforwomen.com) and The North Face Venture ($99; thenorthface.com) use a microporous
Additionally, all of these jackets can be compressed to squeeze into a water bottle and are fully seam-sealed for further protection. So, it's a win-win-win-win situation. What it really comes down to is price, personal fit, the feel of the jacket against your skin, and your color preference.