Hi Chris,
I just bought a Husqvarna YTH20S46LS. Almost brand new with only 3 hours on the meter.
Story goes like this:
Lowes took it back under warranty with a blown engine. I purchased it for $200 AS-IS. The engine was run without oil....or not nearly enough anyway

. After tearing it down and discovering just about anything redeemable inside, was shattered to pieces, I decided to go on the hunt for a long block, 20HP Kohler
Courage as a direct replacement.
After the initial sticker shock for the engine, I started asking around a few local lawn and garden repair shops who, consequently, advised me to not waste my time nor money on the
*Courage engines. 3 of the 4 I visited said basically the same thing. That the Courage model manufactured by Kohler is inherently weak and has design flaws untypical of Kohler's line up.
(*I am NOT a brand or model bash'er !)
Long story short(er), I happen to have a Kohler 14HP sitting in the wings for another project. To my surprise, it bolted right in with very few modifications.
I wish I could tell you how much I love this machine....but my wife took it over the very first day of the engine transplant

! She, however, absolutely loves the hydrostatic drive, nimble agility, power and the option to mow in reverse (something our Craftsman LT4000 doesn't have). She watches patiently for the grass to hint at the 2" growth mark, jumps on the Husqvarna and does most of our two acres in about 45 minutes.
The icing on this cake is, I have another 14HP Kohler in the Craftsman LT4000
The only negative thing I can honestly think of is the 'deck-wash system'. Doesn't work....and a complete waste of time.
Sorry, I wish I could comment on the Simplicity, but I have little knowledge about their line up.
Shartel