Different types of microphones have different uses, obviously. Here is what I have found works best in various situations. Before delving headlong into shotgun mic comparison shopping, ask yourself what will suit your needs the best.
If you want to record specific point sounds at a distance outdoors, including outdoor boom mic dialog recording for film and TV, a short shotgun such as the Sennheiser MKH 416 and friends is going to be your best bet. I wouldn't recommend the Rode NTG-2 unless you're really on a budget, but the Rode NTG-3 appears to have nearly identical specs to the 416. The NTG-3 is a relative newcomer, while the 416 has been the short shotgun mic for at least a couple decades or so now.
If you want to record interior dialog for film and TV, and do a passable job at exterior dialog provided you get the mic a little closer, then a hypercardioid mic is your best bet. Shotgun mics have weird off-axis frequency response as you go farther down the spectrum. Basically the shotgun pattern is only for mid to high frequencies, while the lower frequencies still come in from nearly all directions. Indoors in a normal untreated room, you end up with weird boominess in a lot of cases. This is just down to the various pickup patterns and physics.
Sennheiser MKH 50 Polar Pattern http://www.sennheiser.co.uk/sennheiser/products.nsf/resources/C96939268CC4941EC125743200802EF7/$File/MKH50-P48_ClockfaceDiagram.jpg Sennheiser MKH 416 Polar Pattern http://www.sennheiser.co.uk/sennheiser/products.nsf/resources/B905568D10D34331C125743200802EDD/$File/MKH416-P48U3_ClockfaceDiagram.jpg
If you are recording a scripted independent film and just need a single mic, I would go with the hypercardiod. The Schoeps CMC641 seems to be the gold standard, but it's about $2000. I got an Audix SCX1-HC and have been very happy with it. For indoor dialog I think it sounds better than a Sennheiser 416.
Depending on what field recording means to you, exactly, you may also want a stereo mic of some sort to record ambiences and the like. The Rode NT4 is pretty good at this, and there are several other pricier options from other manufacturers as well. The NT4 is essentially two cardioid mics in an X/Y pattern, so it picks up a much wider field of sound and is less directional than a hypercardioid or a shotgun mic. This sort of mic does a pretty good job of getting a "you are here" sort of ambience with great stereo imaging.
One more note about the Rode mics... their true condenser mics are generally very quiet. The NTG-1 and NTG-2 (but not the NTG-3) are electret condenser mics though, which generally results in higher noise. If a microphone can be powered by a single AA battery, it's generally not going to be a true condenser. Accept no imitations!
Rode NTG-1 and NTG-2 http://www.rode.com.au/images/mics/ntg-1&2.jpg
Make sure and check out this video by Ty Ford where he compares various types of microphones. You can get an intuitive sense of a lot just by watching it.