Personally, I don't care for a PTO model. The main reason being that when the power goes out, it's normally due to bad weather and therefore, the tractor may be needed elsewhere for other chores.
Another consideration is matching your tractor's HP to the needs of the generator. I can't tell what mfgr or size tractor Jason has but would guess it's probably the right size for a 15KW genset. If your tractor engine is over-sized for the generator being used, you're burning more fuel then you need (as you still need to keep the engine RPM's up to get 540RPM to the PTO).
You'll also want to size the genset to your needs. A couple years ago, I bought a 15KW genset and sold my 7.5K to a friend. Well, the 15KW couldn't really do any more then the 7.5KW. Basically, both ran the entire house except the heat pump. The 15KW just burned more fuel (and made more noise). Although I still have that 15KW, I went out and got a 7.5KW as it's the "right size" for most of my needs. I'll use the 15KW once in awhile so Mrs. Zoom can do laundry or whatever but for 90% of the time, it's just too big.
OK, back to your question. I took a look at the Northern Tool offerings. Northstar makes decent generators. BTW, their 7200w for $979 is more then what I paid for a 7500w Honeywell genset with a Honda engine (at Costco) earlier this year.