Merino…
REI carries lots of different brands I imagine. Some popular brands are Smartwool, ibex and ice breaker.
Merino will wick as well as anything but the difference to me is its ability to insulate when wet.
No matter how well something wicks, it will eventually get saturated if you are sweating.
If you paddle hard in temperatures above freezing you will sweat a lot more than you might expect (or at least for me).
If you sweat enough to saturate your base layer then it does not matter how well it wicks…it’s saturated.
Plus…merino wool will NOT stink. In fact I have sweat my but off in some merino baselayers and they emitted no body odor whatsoever (hard to believe but true). Synthetics on the other hand are infamous for stinking profusely from even small amounts of sweat.
Just another consideration…
Another Polartec fan
I like Polartec PowerStretch fleece. Immersion Research makes some nice paddlewear (Thickskin and Thinskin - Polartec Powerstretch and PowerDry). I have some tops in different weights. I also have some Powerstretch pants made by Lowe Alpine and Victorinox (there are lots of other well known bands and lesser known brands that have used this stuff as well). Another option is the paddle wear made by Lochsa Connection(several Polartec products). Mountainsurf used to make great stuff as well (Polartec Aquashell), but I heard they’ve discontinued making clothing. 
They made some of my favorite paddlewear (Aquashell), although used as an outer layer, not under a drysuit.
http://www.immersionresearch.com/
http://www.lochsaconnection.com/
~wetzool
thanks wetz (NM)
doesn’t last long?
I have own Icebreaker pieces that are 7 or 8 years old. They are holding up great and they don’t stink. Maybe other brands aren’t as well made.
synthetics versus wool
I would gently steer you towards synthetics instead of wool as your first attempt. Most synthetics are better at the extreme of safety, because they hold less water. And they’re less expensive. Wool’s merits are more like niceties (to me – it would be different if I got rashes from synthetics): nice feel, lack of odor. If you don’t like the synthetics, you can always pay more for wool later; and if you do like synthetics, you’ve saved some money and gained some durability. With that said, I much prefer wool for my base layer (often with synthetics the rest of the way out).
You can buy nice wool directly from ibexwear.com. I think smartwool.com also sells direct, and it has a dealer list (some of whom stock only the socks, so call ahead). I’m less familiar with Icebreaker. I got my one piece of Icebreaker recently at Paragon Sports in NYC – I don’t know if they ship (but I do know they don’t have good prices).
I agree about Campmor as a retailer. Also check REI’s “outlet” – a different web site from their main site.
I agree with another poster who said that, where your safety is concerned, you shouldn’t take chances, so go with a retailer who knows about cold-water issues. (Or just buy Kokatat’s own line of insulation.) On the other hand, I don’t think the specialists will sell you fleece that’s appreciably different from Wal-Mart’s fleece. So take your risks. I trust you will test whatever you buy with people nearby to help you.
– Mark
My vote is merino wool
it is the material that synthetics have been trying to duplicate since their inception.
‘Traditional’ wool is great but itchy. Along come synthetic fabrics which are trying to be wool without the itch. Then you have merino wool which IS wool without the itch.
more data in a few months
I just got my first Icebreaker shirt and am looking forward to doing a longevity comparison with my Smartwool and Ibex. I read on another thread that Icebreaker is more durable, so I have high hopes.
Have you used Smartwool and Ibex as well? Maybe you just treat your stuff better than I do.
– Mark
I have the kokatat polartec
union suit.
Recently tried the NRS union suit and it is MUCH BETTER!!! Stretchy, comfortable, a better fly (zips both ways, and all the way down) ... and only $53 if you're the right size (!):
http://www.nrsweb.com/shop/product.asp?pfid=2552&deptid=1144
So get the NRS. I'm getting one as soon as my ship comes in.
what weight on the NRS, boh?
do they come in different weights, like the polartec? What one works for you, at what water temp? thanks.
also, I need to try on this kit before I buy it. We have REI here, and several kayak shops, but none carry a huge variety of insulation options to try on. Any other brick-and-mortar retailers to add to the list? We have a ginormous hunting/fishing shopt here i’ll check out, not that I do either of those things.