I have been watching a lot of youtube videos lately and it seem like most of the professional low whistle players are playing either an Overton or Kerry whistle. However, the most recommended whistle on this forum seems to be a MK. It seems like the most recommended and the most played whistles should be the same.
trekkie, Overton/Goldie and Kerry whistles have been around for years and years. Bernard Overton basically created the modern low whistle and defined the sound, and Colin and Phil are in direct line from Bernard. It’s not surprising that their low whistles are a top choice of experienced players.
MK whistles hit the market really only 3 or 4 years ago. And I think Misha doesn’t make that many, since he’s also a full-time musician (Croft No. 5 etc.), designer and writer in real life. So you can do the math.
Of course, most professional musicians play neither. 
Also, recommendations on the Chiffboard may or may not bear a resemblance to the real world. 
People play whistles that they like, regardless of whether or not they play professionally. It’s a matter of personal preference - based more how a whistle responds to an individual’s style of playing. Not all whistles are the same for a reason - because not all whistle players are the same. I’m no professional at all, but I can tell you that I’ve kept the whistles that I have, because I like the way they play in my hands, and not because of the name stamped on the tube.
The makers of Kerry whistles post many videos on YouTube of famous players (whether they are playing Kerry whistles or not). That may add to the idea that a lot of professionals use them. (I’m not saying they don’t)
I don’t know of any professionals who stick to only one maker. Seems to me that perhaps Overton/Goldie and Burke are the most common among top players, but there are a lot of great whistles and whistle makers out there.
Overtones where perhaps the first high quality low whistle out there to be marketed to the ITM crowd. I know I started my whistle making career because I wanted one and couldn’t afford it.
Also, recommendations on the Chiffboard may or may not bear a resemblance to the real world. >
hahahahhaha! 
Phil Hardy has told me that he’s not responsible for the clips on Youtube, so just wanted to clarify that for him.
I know if I were a professional musician, I’d definitely use a Goldie or a Kerry Pro, no doubt, without question.
This is ground which has been covered before, but when this topic comes up, and people use the word professional, I need to point out that many of the people playing whistles professionally, that is, making their living at it, are the nameless faceless studio musicians and other working musicians whose main instruments are “legit” woodwinds (sax/boehm flute usually), and who “double” on whistles. These working musicians show up at gigs with bagfulls of whistles, bamboo flutes, quenas, panpipes, etc etc because they never know what sound the composer wants.
I have worked with this sort of person many times over the years and 1) they invariably know nothing about Traditional Irish Music, nor do they care and 2) they tend to play off-the-shelf Generations, often horrendously out of tune, whistles which no good Trad player would use. (Having Perfect Pitch, they effortlessly play these whistles in perfect tune.) Occasionally one of these guys will have a full set of Burkes or Kerrys in every key. (Laying out a few thousand dollars is nothing to them… it’s a writeoff anyway).
I would hazard to guess that this sort of player far outnumbers the “star” traditional musicians, the few who are able to make their living playing traditional music.
Quite a rant! Doesn’t trekkie mean whistle players who play full time? You don’t get many of the players you describe this side of the water.
I probably should have used the word performing instead of professional as I intended to refer to musicians who were accomplished enough to perform for an audience or record even if they don’t make a living playing.
I’d certainly mention Copeland and Reyburn, along with MK, Burke, Overton/Goldie and Kerry Pro as low whistles often used by performing musicians. Seamus Egan is now playing a new model Reyburn as his main low D, in preference to his Copeland. Some of us like the lower back-pressure whistles over the Overton types.
What is the back pressure of an MK? It’s my only low whistle so I don’t have anything to compare it to and I’m curious if other whistle brands would have more or less back pressure.
One thing I like about Reyburn whistles is the plastic mouthpiece. Seems it would warm up quicker and have less condensation.
I would guess that’s partly because his Copeland low D is now in someone else’s hands, having been stolen in Dublin in 2006 and not recovered (as far as I know). 
But that certainly doesn’t discount his choice of Reyburn as a replacement, as I’m sure he could choose whatever he wanted.
Seamus Egan may be playing the new instrument because of the impossibility of getting another Copeland efficiently. There is no doubt that it indicates he likes the Reyburn, but I think it would be wrong to decide he likes it better than the Copeland.
That said I have 3 very different low D whistles: Copeland, MK, Onyx. Each is a lovely thing to play and each has a different tone quality. The Onyx has closer holes on the lower hand, and the other two are about the same, so if I play the Onyx for a bit going to the others can be a problem until my hands readjust. The Onyx doesn’t plug much at all. Both of the others should, like most metal whistles, be warmed up to avoid plugging. The issues of upper octave tuning adjustment are different since the Onyx and Copeland are reverse conical and the MK is cylindrical. The C’s are all a bit different too. But all these differences are easy to adjust to and the sound differences and fine quality of construction make them a joy to select from.
I recently bought a Goldie Low D from Colin. I already have a Goldie High D and like the medium back pressure so after discussing it with Colin I bought a Low D with the same medium back pressure. Colin tailors the Low D to your requiremants meaning that you can have a low, medium or high back pressure whistle.
The MK I recently tried had much lower back pressure than the Goldie that I have.
My first Low D was a Dixon Tuneable plastic model. It has very low back pressure and is a quiet whistle but with reasoanbly low air requirements.
I also own a Shaw Low D which which I hardly ever play. It has a very high air requiremant and there’s no back pressure at all. If I play in the upper octave for any length of time I end up getting very dizzy. 
A friend recently asked Seamus Egan about his new Reyburn. He reportedly likes it very much. He has tried a few used Copeland’s as replacements, but they were not as good as his old one. There are variations within any make of whistles.
The Reyburn and MK are medium-low back-pressure whistles. There is some back-pressure so you can get through a phrase in one breath. I prefer this amount of back-pressure and have not tried a Goldie with this low of back-pressure. Higher back-pressure whistles are not my cup of tea, nor are the very low back-pressure whistles.
Thanks for that info, Ted!