I personally think Leatherface from the Texas Chainsaw remake (think the origional is a bit cheesy) followed by Jason.
Leatherface in the remake is extremely intimidating by comparrison to the origional and the bit in the locker room near the end of the film had me right on the edge of the seat. The first 4 Jason Films were the best I thought as they all followed on from each other pretty well. After that he started getting resurrected in each film and it got a bit silly really. Love the twist in the oigional Friday 13th, it was the last film I actually saw out of all of them (seen them 3 to 8 then the first 2).