I would say hands down BTC and then .0XX01 denominations. Newcomers will find mBTC and uBTC a little confusing and sometime I forgot what they stand for. This isn't even considering the more uncommon denominations. However, what I do think would be nice to make things more clear are more integrated BTC to USD/EURO/RUS converters. That way people have an easier way of visualizing what .0158 bitcoins is actually worth.
you're probably american, because the rest of the world is pretty much used to using the metric system (including m and µ) in everyday life.
It's not much different from using dollars and cents. Instead of cents (from centi, meaning 1/100 (also 'per cent' comes from this word)) you have mills (from milli, meaning 1/1000) and mikes (from micro, meaning 1/1,000,000) if we ever need to we could even go as far as using nanos/naan/nans or something (from nano meaning 1/1,000,000,000) or picos/pics (from pico, meaning 1/1,000,000,000,000) there's a whole lot more but these will probably be sufficient for the next couple of decades.
(there's still femto, atto, zepto, and yocto left, i'm not sure if there's anything after yocto but then again it may never even be needed)
Yep. No confusion will come out of all those names for sure.