Thanks for joning us here and Welcome!
Depending on your usage, any one of the three you listed would probable be fine, but there certainly are advantages to each unit you are looking at.
LT2000- parts are easy to come by, and readily available. Not Knocking the new Sears / Craftman stuff, but this is a lightweight and lighter duty machine, the least of the bunch. - Disclaimer - I have a DLT3000, good machine, not great, but good enough for mowing.
The 4500 is a step up , and if you have the need for the increased width of cut, not a bad choice at all. Still a light garden tractor though, IMHO.
The Case 448 is a step back in time, yes, but overall is more rugged, durable and one can get a whole lot more attachments for it. The Onan motors are a bit thirsty, so there is a drawback to them in that regard. The grass cutting abalities are fantastic, and overall, I would not hesitate to vote for the 448 being at the top of the list. -- disclaimer- I am a Case 222, 448, and 648 owner / user....
Edited by marlboro180, November 05, 2012 - 10:54 AM.