Ok I would get the F 350 ( i will tell anyone to get a 1 ton over a 3/4, I don't care what brand you are looking at, i still would recomend the 1 ton). It is not that the 250 isn't a good truck. It just i belive that the 1 ton pick up for a little bit more ( the base cost for a F 250 4X4 is around 23,400, the base cost of a F 350 is around 23,900, this is for regular cab 4X4 XL before adding options) So the F 350 isn't that much more.
Ok, as for an engine, the 5.4 will work fine for plowing, and light towing (for a regular cab, anything else go with the v-10). However if you plan on pulling anything heavy move up to the V 10. In my personel truck, a 99 F 350 4x4 regular cab, I have the 5.4, works fine for plowing, and the fuel millages is good for driving around. However they day i had the max payload in it, was the day i wished i had the v-10 ( i have enough other trucks that can haul heavy weight, so most of the time, i don't carry more than 500 lbs in the back.) If this is your primary truck, and you plan on carrying a v-box get a V-10 and Get the F 350.
So let me sum this up.
If you want great performance when:
Towing over 3K
Freighting a V-box
Hauling a Heavy pay load
Get the V-10, auto, 4.10 rear end
However if you are not going do the stuff above, very often, the 5.4 would do the job.
However i think my next truck will be a diesel, only i guess you have set your mind against it.
Geoff