I know many people like merino tops and in my opinion icebreaker is excellent. I am a large chap and agree entirely that this is less fitted and suits the less athletic. It retains its shape well and really doesn't smell (I have tested this!!). I have several items and have found that the very thin stuff (150, 200) is the best for me as you can easily layer it. I take a long sleeve (200)and this short sleeve out with me walking and skiing. I have found they work like the base layer equivilant of those three-in-one jackets. My only note of caution is that both the 150 and 200 tops are thin and they can snag on rucksacks etc if you're not careful. Icebreaker do an excellent 260 weight baselayer as well which I prefer when it's a bit colder.
(Written by: Fat,Bald&40+)