It's a moot point, heads I win tails you loose.
The kawakasi is supposedly a better engine but I don't see much difference.
Kawakasi parts are a lot more expensive than Kohler parts.
if you are not punishing your mower both should do the job standing on their heads.
Run both and listen to the engine, from what have seen the kawakasi has a better muffler.
Neither have what I would call a great air filteration system. but the Donaldson type double element filter will bolt strait on the kwakka and the Surplus Center is currently listing them for less than what I pay for the filter elements.
What I don't like about them is the spindle housing , part 14 in this diagram
http://www.ereplacementparts.com/husqvarna-yt46ls-96043015000-garden-tractor-parts-c-114486_117796_290409.html the mounting is not good , they break at the arms when the bolts are and require cleaning to work properly.
As for a large deck. they can be more of a curse than good.
The bigger the deck the more it will tilt when you turn thus tend to scalp on the inside of turns.
Scalping is also worse on "undulating" lawns.
Then there is access to small spaces .
Work out the width of you yard then divide it by 44", allowing 2" overlap each pass ( 6" is closer to the point ) but leave it at 2 for now.
That is the number of passes you will need to do to mow your lawn with a 46" deck
Then do the same using 40" that is the number of passes using a 42" deck.
Usually the difference between the two numbers will be less than 1.
In many cases using a wider deck actually takes more time than a smaller deck particularly if using the wider deck means more hand cutting with a push mower or trimming with a line trimmer.