The most important thing is getting the PTAC that delivers the proper BTU's of heating and cooling for the space. This is done by a contractor performing a heat load and loss analysis on the individual living space.

As far as brand goes, I can't comment since my experience with PTAC's is nil. Hopefully some others will. As long as you get a good warranty, any major mfg. of this type of equipment should be okay...

It's a little like buying a car - you can go for the economy model all the way up to the Cadillac.

Lowest cost would be a through-the-wall unit similar to a window a/c unit. This would probably cost $300 or so. It could be integrated into the construction so it did not look so much like an add-on, and there are some units I've seen in single-room applications like this that look pretty good, both inside and out.

Next would be a motel-style unit, often sold by GE under the model name Zoneline. Other companies have similar units. This could have heat strips for heating, or you may not need them since you're going to have the in-floor radiant heat. I think if it were me I'd get the heat strips because it's not going to cost much more, and gives you a secondary heat source. Cost here is probably $600 to $800.

Best would be a mini-split unit like a Mitsubishi Mr. Slim. This would be quietest, as instead of one unit you'd have an inside unit and a separate outside unit. The inside panel would look a little like the inside panel of a window a/c, but it usually is positioned up higher on the wall. This is quietest because the compressor is removed from the inside unit, so all you hear inside is the fan, but you do then have to have a place for an outside unit (smaller than a standard outside a/c unit) somewhere reasonably nearby. Cost here, given this is a single room with likely a fairly small capacity needed, would probably be $1000 to $1500.

I'd see what your architect thinks, as well. because since this is new construction you want to do this right, and aesthetics are going to be an issue.