Are you talking about hand-held interviews? That is one of the most common uses for omni mics in field recording. Another is small omni lavaliers. What type of field recording do you have in mind?
Also, by "field recording" do you mean indoors or outdoors. Omni's are best in studio situations with controlled reflections and little or no monitor audio. I can't imagine a situation where I would use an omni outdoors, with traffic, nature, wind, and overhead noise. In that situation, I would mic every subject with a cardioid.
The RE50 is a very common field interview mic. Same with the 635 Omnis are great in outdoor applications, not just studio uses.
They work well in handheld, or short boom applications where control isn't as easy as you might like. They also help in interviews to minimize the differences of proximity and axis when it's a fast interview and the mic is being moved back and forth from interviewer to interviewee.
I prefer the AT 804, as it blends really nicely in a stereo/mono mic situation, and does well for really nasty situations where you might be worried about the mic being damaged. It's a nail-pounder for sure. It's also priced right at sub 100.00
I use and really like the Azden SGM-2X. It is a shotgun microphone that comes with two barrels (and two windscreens) - 1 that is 8.5" long that is an Omni and one that is 15.75" long that is Super Cardoid.
It ships with pretty decent shock mount and the audio quality is quite good - especially with base boost (switch on barrel). I have owned and used an ME-66 and while this isn't quite that good, it is very close.
Make sure you get a Shure A96F line matching transformer to be used with mini jacks like on FX1.
Purchase price is $239 from B&H in NY. The A96F is another $37.
MD42 reporter's Handheld with a "butt-plug" Tx - great to allow your interviewer to wander about. This mic allows for the interviewer to place the mic "between" some not needing to wave it about. HOWEVER . . waving it back and forth does give the interviewee a "cue" to speak! Now THAT I just realised only in June this year! LOL!
Lapel/tie with its Tx. Was up a very noisy building site this week. Talent can be heard plain as day.
The Senni66? What can I say .. it is good for a small range of requirements. It was my initial mic I bought back in Nov'02 and saw me thru some noisy environments. I've got some splendid recordings of blackbirds . .. which then needed to be "washed" thru SF. . . er . . . it provides that "other" fill if needed .. . er . . I CAN use it when being used in conjunction with a Rycote pistol grip . . er . . to me, it is a very "bright" sounding mic . . . oh yes, I've used it raised high on a light tripod to get some "sweet" recordings from a 2-hander, in-the-round-stage presentation. It was VERY good for that.
I've been listening hard to DSE, farss, Chienworks, Ty Ford, - that there isn't a mic for all Seasons and I stopped bashing myself over the head thinking that all I need to do is do audio-post improvements - eh, no! I realise that I DO need to experiment=MONEY, unfortunately, with getting an ever growing arsenal of audio kit - was it ever thus with this "sport".
I'm planning to record the "ambience" for a personal sound effects library. Some examples are train stations, traffic, popular parties and so on. I'd like to get the best quality possible. Most situations are outdoor locations, but in some cases it may be indoor sound capture.
Now here is a different scenario than what was originally assumed by myself and other posters....
So, if it's for ambiences, you want stereo. For best stereo, particularly outdoors, you'll probably want uni's, only because they'll have a proximity effect and cut some bass out that you likely won't want if you're near roadways, etc. But if you're looking for the most pure sound, then a pair of omnis is the ticket. Spread would be determined by the sound you're after, whether in an X/Y set up or an A/B setup. For this sort of thing, I really like the Giant Squid stereo kit. We recorded over 200 ambiences for a convoluted reverb library using the Squids. We loved em', and the software manufacturer loved em.
I was astonished over the quality of a pair of Oktava MC-012s in X/Y configuration, used them for a live event a few years ago.
This is a moderately priced russian microphone, but it's hard to find the genuine article. Many poorly made copies made in China and sold with fake Oktava labels.
Oktava USA claims to have the real thing. The current version of what I used seems to be the MK-012.
I have used my AT822 stereo mike more than any other mike for my camera. It comes with adapters for practically every need including an XLR to 1/8" stereo plug to go straight into a camera and an XLR to two 1/4 " plugs for L&R inputs. I also made a special cable to plug it into two mic inputs on a mixer. It sounds great as well.
Currently the best price I have seen is from 8th Street (reputable) at $239.
I absolutely love my Audio Technica AT-825, which is the balanced version of the AT822 that John mentioned above. It is amazingly versatile and sounds terrific. I highly recommend it (or the AT822.)
I too, love my AT, also really enjoy the Rode NT4. Heavy sonuvagun tho. Myself, Randy Stewart, and Colton Steward recorded several hundred reverbs for a convolution reverb system using both the 825 and the NT4, and they sound wonderful. The NT4 is just a touch hotter, with better bottom end, but the AT is slightly smoother and more accurate high end, IMO.
I've been using an AT822 for many years with my portable Sony TCD-D8 DAT recorder (sponsored by Duracell!) and like it a lot, but for picking up ambience the Oktava MC-012 beats it by a wide margin.