Couldn't be happier with my Huub Albacore and ticks all your boxes. Least restrictive wetsuit I've swum in and I was in a Helix the last few years.

Roka Maverick pro

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-shoki

De Soto is great for me

Regardless of the suit you go with the most important thing is to get a suit that fits. Fwiw, if you don't like your Nineteen, before tossing it, you might purposefully trying stretching the neck and maybe even breaking some fibers in there. I have done that with plenty of suits. My 2XU suit has had probably the lowest neckline I can remember but I still stretched it as well. If you want a suit with super thin shoulders I do recommend the BlueSeventy Helix. If that is something you end up wanting to go with you can save 25% here. BlueSeventy has a very generous return program if the suit doesn't end up fitting.

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I just got the Zoot Wikiwiki. It has the thinnest arms/shoulder material at 0.5mm, that I've ever felt. It's crazy... I suspect it's as close to feeling like a sleeveless wetsuit as a full could get. The materials are super soft and stretchy. I have been babying the thing for fear of easy ripping, but so far, so good (only one race and and one training swim).
I was also looking at the Blue Seventy top end suit (helix, iirc), but went with Zoot mainly bc it was cheaper. I also liked the brighter colors and reported comfort/flex in the shoulders... Which I can now confirm!

Blue Seventy Helix

A two piece like DeSoto might help minimizing the shoulder restriction.

I went from Nineteen Rogue to Roka Maverick Pro and I found it similar but better in slight ways in areas you are looking for. Lots of freedom in shoulders and feels good around neck. I've owned a lot of suits and this is the best one for me and I've done a few swims year over year faster in the Roka for what that is worth as each day can be different.....

Like Canuck1, I’ve had a few suits as well. Currently I have Roka Mav and Roka Mav II. I purchased an Xterra Vortex with their google special ($200!). I wore it once, loved it. The prob is my son tried it on. (We have a real nice lake near us so he, my wife & I OWS a few times a week). Anyway, the son has kinda taken that Vortex, I’m seriously thinking about ordering another.
From a comfort standpoint both Roka & Xterra are very comfy & flexible.

People seem to not like Xterra but their vengeance wetsuit is pretty nice and they usually have some sort of sale.

Roka Mav Elite's and Pros have worked great for me the past 2 seasons.

This ^

Love mine. Fits the bill for the things you're looking for. If you're between sizes, go up a size for comfort... especially if you have trouble with feeling 'constricted' normally.

Xterra wetsuits are absolute crap.
I’ve been making custom wetsuits & repairing & altering wetsuits for over 40 years now. My company is quite possibly the first custom wetsuit maker in the world (1954)
I’ve repaired 100’s of Xterra suits that should have been guaranteed by Xterra.
Xterra are the worst manufacturer ever, their customer service is horrible, and the whole lot of the San Diego employees, owner included are liars & cheats.
The suits are made in Cambodia & cost Xterra less than $25 total. The Neoprene they use is fragile at best & Xterra will tell you all those little crescent shaped rips are your fault, they are NOT your fault, it’s the fault of Xterra using crap material, those are stress fractures.
DO NOT buy an Xterra wetsuit under any circumstance.
Find any other manufacturer, but I repeat, DO NOT buy Xterra.
Mr Rubber.