I'm making this choice too.
NGP vs Otterbox (reflex or commuter) vs Eclipse.
Eclipse looks the nicest to me and it seems like it offers decent drop protection.
I might be able to chime in on the NGP vs. the Commuter. I've got both and they're both very nice cases.
The Commuter is my favorite case (dating back to my 3GS). Great drop protection, works perfectly with a screen protector, and has the nice built-in port protectors. Also, no flash issues. As it has been beat to death on the forum, they've updated the silicone with a firmer style that can be finicky at first when it comes to getting the plastic shell to sit correctly, but I've found that with use, the silicone becomes more pliable and works perfectly. I actually prefer the updated silicone now (I didn't at first) because the firmness of it keeps the part along the sides (that's not supported by the plastic shell) from being too flimsy. My only real gripe with them now is that the updated silicone no longer has small plugs that actually go into the ports...they're literally just covers that sit on top of them. I'd like to see them bring the plug-style port covers back. It does add a bit of bulk to the phone, but nothing like the Defender, and because of the plastic shell over the silicone design, it slips in and out of a pocket easily.
The NGP is also very nice and deserves all the praise it gets. It's got a great in-the-hand feel. I would liken it to being right in the middle between a silicone case and a TPU case. Firm enough that it doesn't flex much, but soft enough that it's not going to scratch the phone. You also don't have to worry about it catching lint or having flash issues. When I first put it on the phone, the corner near the mute switch wanted to VERY slightly lift the screen protector, but after massaging it just a bit, it stopped doing that and hasn't done it again when the case is removed and put back on the phone. I would surmise that it also offers great drop protection, as the corners are nice and thick, but not so thick that it makes the phone huge. I've got the smoked version, and I love how it's transparent enough that you still see the Apple logo on the back and can see the steel band on the sides and top of the phone. I like to keep my ports covered, so I use a 30-pin and headphone silicone plug to keep them protected. This case works great with them. My only real gripes about it would be the piece that runs between the 30-pin port and the screen, just below the home button. It does feel just a slight bit flimsy and I don't know if this will worsen over time. I haven't seen many reports of it, though, so it may just be me being OCD...lol. And the headphone opening on the case could stand to be just a bit larger. As far as size goes, again, it adds a little bit of bulk to the phone, but not enough to worry about. I also don't have any problems getting it in and out of a pants pocket.
I don't think you can go wrong with either one, really.