Since the people actually knowing much more about this than me seem largely reluctant to put it into any answer, I'll give it a first try by linking to some external resources that might give some insight into the matter. First of all the movie itself was shot on a mixture of 65mm IMAX film and 35mm film.
The official site of the movie gives some further explanations about the different formats you can watch the movie in:
IMAX® 70MM FILM
When presented on IMAX 70mm film, the sequences shot on IMAX are printed full quality in their native format- the highest quality imaging format ever devised, offering almost ten times the resolution of standard formats and filling the giant IMAX screens from top to bottom. The 35mm anamorphic sequences have been blown up to fill the IMAX screen side-to-side using a 6k digital DMR process, the highest resolution processing ever used in a feature film presentation. The finished picture switches between the 2.40:1 and 1.43:1 aspect ratios at key dramatic moments in the film. This is combined with a specially made IMAX uncompressed sound mix for the most immersive presentation of the film.
The digital IMAX presentation has been created from 6 and 8k scans of the original film elements, graded specifically for the high contrast IMAX dual-projection system. When presented on digital IMAX, the sequences shot on IMAX will fill the IMAX screens from top to bottom and switch from 2.40:1 to an aspect ratio of up to 1.9:1. It will also carry the uncompressed IMAX sound mix of the film.
When presented on regular 70mm film, the IMAX sequences have been optically reduced to 70mm 5 perf film to produce a grain-free, ultra-high resolution image, cropped top and bottom to fill the wide screen. The 35mm anamorphic sections have been blown up optically. Both processes are photochemical, preserving the original analog color of the imagery and combined in a 2.2:1 widescreen presentation. The sound is carried on a separate Datasat disc to produce state-of-the-art 6-track digital sound.
The 35mm anamorphic prints have been made photochemically, preserving all the rich analog color and high resolution of the original 35mm anamorphic photography. This is combined with new 4k negatives produced from 8k scans of the IMAX original negatives, cropped top and bottom to create a seamless 2.40:1 scope image. The sound is coded on the prints in Dolby SRD for a 6-track digital playback experience in most theatres.
The digital presentation of INTERSTELLAR has been created from 4 and 8k scans of the photochemically- color graded film elements, fine-tuned in the digital realm to maximize the color and contrast attributes of digital projectors, and dust-busted to achieve the cleanest and most stable image presentation possible. The film was mastered in 4k for the highest digital resolution currently available.
In addition to this more technical list, there is also a more judgemental characterisation listing the formats in the preferred order of this article:
1. 70mm IMAX (film)
If you like Matthew McConaughey as big, bright and clear as technologically possible, 70mm IMAX is the surefire way to go. Nolan loves to shoot as much of his films in IMAX as possible (the massive cameras limited him to a little over an hour's worth of Interstellar), and the result is a clarity and depth of field that, in many ways, beats even the best 3D in terms of seeing into the picture.
The individual image frames of 70mm are actually 65mm (2.6 in) wide, with 5mm set aside for magnetic sound tracks. The format boasts almost 10 times the resolution of standard projection formats, which is especially important when you're blowing it up on a full-sized IMAX screen. Standard screens are roughly 72 feet x 53 feet, but can be as large as Darling Harbour in Sydney, Australia, which is 117 feet x 97 feet (and will be showing Interstellar starting Wednesday).
2. 70mm (film)
This has all the benefits of 70mm; it's just not blown up on the big, big screen. "Standard" movie screens vary widely in size depending on the size of the auditorium, from inching up on IMAX-sized all the way down to about 50 feet wide. You'll still be impressed by the clarity, light and high definition, which is still three times the resolution of standard formats.
3. 35mm (film)
This is the next best thing, and it's still considered by many as superior to digital projection. With nearly 200 theaters worldwide (most in North America) showing Interstellar on 35mm, it should be easy to seek out.
4. IMAX digital
Most commercial, wide-release IMAX movies are shown this way, and most of us would never know the difference. The process involves two projectors that line everything up with lasers for great precision of both image and sound. But in the same way that CDs just aren't vinyl, digital just isn't film.
5. 4K digital
Almost all major movie chains project digital in 4K these days, so it's less likely that this will be offered as an "option." Either your theater is 4K or it isn't. If it isn't, at least you're seeing it in...
You probably also always fly coach, rent economy cars and couldn't get by without your Costco membership. Either that or you live in Palookaville. Or both. Nothing is wrong with either: You'll still see what it's like to enter a black hole, and by the time you get there, you'll have long since forgotten that the Big City movie snobs saw it with a little more clarity.
But now it is on you to judge what format offers the best tradeoff for you regarding observable image quality differences compared to time and money costs and I guess only some existing real-life experience with the resulting projections could help you in this regard.