JD, a lot of the decision could relate to the types of detecting you do, Coin Hunting Vs relic Hunting, and the locations and conditions you're likely to encounter.
I have used all the coils you mentioned, and I prefer to stick with coils made by the detector maker. I have the used the RC26, which is the 5½X10 DD solid-body coil and it worked OK. There are some of these coils still out there available, but I believe they were going to be discontinued due to the replacement coil, the RC24, which is an open-frame 5X9½ design, and similar-looking to the Fortune and Sharpshooter.
Of the three coils you mentioned, all of them work just fine and I would say the primary difference is that the RC26 is the solid-bottom design which can help eliminate snags when hunting in short, stiff weeds and brush. Some people I know have both an RC26 and one of the other two in their coil arsenal. Some also kept the RC26 solid coil and added the RC24 open-frame design.
Personally, I like the field performance of the new '24' and also have the FC24, FR24 and IM24 mounted on, or on a spare lower rod for, my Nokta CoRe, Relic and Impact. It's all a personal decision of what coil an individual feels might fit their needs the best. Of the mid-sided DD coils available for the Racer 2, my personal pick is the RC24 that is very similar-looking to the NEL and CORS offerings you described.
However, if you have a smaller coil for really tighter, densely littered sites, and if you're mainly looking for a mid-sized search coil, let me also suggest you consider the newer, round-shaped RC18C which is the 7" Concentric coil. If I had to narrow down to only one search coil to own and use for either a Makro Racer 2 or Nokta Impact, it would be their 7" Concentric coil. It is roughly 2" shorter in front-to-rear length but 2" wider in width than the RC24, Fortune or Sharpshooter coils, which is kind of a trade-off. Plus it offers the benefits of a Concentric coil design.
Not certain what you want a new coil for so there are my thoughts and suggestions.
Monte