The Tiger Cat is a newer version of the Cub, as M/M mentioned. I have an older Scag Tiger Cub with the 19hp Kaw engine. Been a fine product. I bought it because it was the best value when shopping around, and I think the Kaw engine line may have been the exclusive offering for the Cub at the time (that is obviously no longer true for the Cat)? It was the only engine I saw on all the Scags I looked at, but that was like 12 years ago ...
As for the engine choices today, I would not hesitate at all choosing the B&S engine for that model. That engine series is not your run-of-the-mill B&S that you'd see in a low dollar unit at Lowes or TSC. The Commercial engine is very well built; see this site:
Scag Commercial Turf Equipment - Vanguard Engines
The Vanguard engines have been the top-of-the-line offering from B&S for years. Very robust.
My neighbor just bought the top-model of the Simplicity (called the Cobalt) and it came with a B&S Comm Turf engine on it. Both the mower and the engine seem very well built; solid and strong. Although he's not got a lot of hours on it yet, I see no reason he'll not get perhaps 20 years out of it mowing his 5 acres. I would be honest and say that it's built every bit as well as our Scag commercial units.
Here is the Vanguard site:
Vanguard Commerical Power Engines | Vanguard Engines
Most, if not all, Vanguard engines come with forged connecting rods, fire-ringed head gaskets, etc. These are BUILT. These are NOT your Sears Craftsman el-cheapo engines.
It's not really fair to compare the CommTurf B&S to the lesser made Intek and such junk they offer. Those lesser grades are POS, IMO. My son has a 20HP Intek VTwin that he's toying with in his racer/mower and it's been a PITA. They are not built to last. Conversely the CommTurf is a Vanguard product and it's their top offering. I have read much about them and they seem very well made.
Now, I do believe the Koh and Kaw engines are possibly a bit better, but to be honest I think they are all so good it would be very difficult to distinguish the variances between them overall. Let's not pretend like Koh and Kaw don't occasionally have engine issues, either. Kaws in particular seem to like to burn up ignition coils at times ... Koh's can have some valve seat issues. The lesser grade Koh's (Courage line) is, to be polite, "iffy" and I'd rather rebuild an old engine than use a Courage. Even the Kaws have differing grades. The FS, FX, FD, FR, etc.
I'll note that as of this date (Jan 2015) even the Kaw offerings are different depending upon mower size; that's a concept I don't really understand ... Why is the Kaw FS offered in the smaller 48" Cat mower but the FX motor is in the 61" Cat mower? Why the "best" engine on the bigger unit in the same freakin' product line??? If I were to buy a mower today, I still would want the FX motor, but perhaps in the small deck. Why does Scag offer the higher grade engine ONLY in the larger deck mower of the same product line???? That just befuddles me to no end; I cannot explain it. If I understand correctly (and I may be wrong for all I know), the FS and FX are essentially the same or extremely similar, EXCEPT that the FX uses the external cyclone air filter whereas the FS uses the integral "normal" air filter. If I wanted a smaller deck, but was going to use it commercially, why not offer the FX with the 48" deck? For homeowner use it probably would not make any difference, but for commercial use the "better" filter would be something I'd want.
Essentially, when you pay for a commercial grade mower, you're going to get the top engine offering from each engine brand. The Vanguard is a very good line. As good as the Kaw? Meh ... maybe so, maybe not. But they are all good engines in their top offerings. I don't think you can go wrong with any of them.
Bottom Line suggestion:
If you are only mowing personal acreage at home, and not mowing commercially for 40-60 hours a week, then I'd not hesitate at all getting the B&S engine as offered in the Cat.
If you are going to flog that thing with a mowing crew you employ for 10 hours a day, six days a week, I might tend towards the extra expense of the Kaw FX engine.
Since you indicate it's 5 acres once a week, the B&S CommTurf should last you a LONG time. Why not save the $2000?
