IMO the Zoom H4 is the better product.
I have an H4 and also an R16 (16 track, record on 8 simutaniosly).
A friend has the Boss Micro, but is thinking of changing it for an H4,
after having used mine :)
For multi tracking, I think you would have to go some way to beat the
R16. It is very good value for money, with a street price of not much more than an H4 !
It runs off batteries or a wall wart, and also has 48v phantom power on 2 of the
8 inputs for studio mikes.
I use a PC (ProTools) for mixing and mastering (the R16 also has a USB port to enable you to use it as a control surface); but I find that the 'transparency' of the R16 (just push the red butto 8)n ), allows you to get on with the music making, and not have to keep interupting the creative flow to swop your 'artist' head with you 'studio engineer' head :)