I find that the easier unit is the BTC, mBTC can also be useful when you're measuring smaller amounts, like a coffee or food.

I am pretty accostumed to use BTC and satoshis, but when I see a quantity written in bits (for example) I have to do some mental math to get an exact idea of the value.

Also with BTC amounts not including the trailing 0s, I get a little confused. For example 0.000076 BTC is more confusing than 0.00007600 at least for me.

Many folks are comfortable with two places after the decimal point.  So with μBTC one Satoshi is 0.01μBTC making the Satoshi a little like a penny, especially when 1BTC=$1,000,000 or rather 1μBTC=$1.

+500

I hate when they cut the last of the decimals off.

BTC is for me the main unit I am using. When I have to use satoshi or other unit I need to recalculate it
If I would vote for second I would chhose mBTC.

I am most comfortable with bitcoin and satoshi. I don't know why, probably because I've been using both since the beginning I started with bitcoin. I might start to change these things since they use different measurings on gambling sites and such.

Obviously, BTC.

End of opinion.

Satoshi up to 9999 (when people say stuff like 500K satoshi I don't process it) and BTC for everything else online. It's awkward saying "point-zero-zero-one bitcoin" in actual speech though, so maybe mBTC could get a better name than "millie" and we could use that?

I'm much comfortable when using the BTC itself as it's own measuring unit. It just makes me get really confused all the time when I see on other websites that they use smaller measuring unit and I have to use an online converter just to understand how much exactly it is in order to not get confuse. It's just makes the process a bit longer if other units used.