I have found that $50 Propper base layer shirts are really nice. They are 5% X-static thread, which is a silver imbued thread that prevents microbial growth.

Seriously, you can take a shower, put on deodorant, put on this x-static shirt and go hiking for 3 days in it and you won't stink. Not from the armpits anyway. The x-static shirt is also paneled for your sweat regions to both wick away and evaporate sweat quickly. They stay dry and cool you off when it's hot, and provide a little bit of insulation when it's warm.

I'll be hiking in Florida, 75, 80 degrees, sweating, and the shirt is cooling me off from the sweat panels. at above 80 degrees you're gonna want to take it off.

If I'm wearing the base layer shirt under a t-shirt, I can ride my bike in 55 degree weather without much of a chill.

I have 5 shirts already and I wear them almost constantly. I wash them after each use and they are holding up beautifully. This is one expensive piece of gear that is seriously valuable.

Here's the best price I've found. $45

http://www.vtarmynavy.com/lightweight-apcu-long-sleeve---black.htm

I think it's like $53 shipped.

I am 5'11", male, and weigh 190, and I find the XL size fits right.