Hey Marauder,
About small vs medium vs large weapon, the whip is rather small, after all; Indiana Jones had it looped on his belt and it never got in the way. It's 15 feet long sure, but it doesn't weigh that much.
As for what it is, it's a melee weapon (I get to say things like this in the house rules forum!
) upon which Weapon Finesse may apply. It has a 15' reach, and it doesn't threaten any areas. It may be used to attack foes adjacent and those at a range. So what if it deals subdual damage: whips will cut skin but the pain is more signifigant than the damage. And it certainly won't get through platemail. I like the whip (damage wise) as is. You have to be clever to use it effectively.
Try combining using a whip and the Use Rope skill: instant 15' rope that can be untied from what it's anchored to with a flick of the wrist.
Whip + Animal Handling: Animals learn tricks faster.
Whip + Climb: More Indy goodness
Whip instead of Disable Device: Set traps off from long range.
Whip + Heal: Can be used for a tournequet in dire straits.
Whip + Intimidate: +2 to +4 circumstance bonus. That snap is scary!
Whip + Perform: Sigfried and Roy!
Whip + Ride: Get the most out of the hitched horses.
Whip + Jump: ever play Bionic Commando?
Last but not least; if you're starving, you can eat it!
Whips are great!