In this guide I'll be outlining good pubstomp heroes.

How to play them is found [Hero] Mini Guides for all 66 Heroes - Heroes of Newerth Forums
I'm sure most of you know that post but refer to it for the builds for most of these heroes.

First off I want to say, if you are going to follow this guide and pubstomp your way up the PSR rankings it is NOT good idea to push it past your true skill level. Also specific tactics in this will only work on the 1300 - 1550 level. I'm working my way up at the moment and will update given how it fares in higher levels. I, and I'd think a lot of people on iO have less then great PSR's due to bad pubs and terrible teammates.

I for one have seen engineer's getting Helm's. Witch Slayer's getting a scarab first item. Moonqueen's with 2 wingbow's. I've also seen almost everyone on my team as an initiator that has a portal key and they've had full vision of the entire enemy team and they let hellbringer drop his malphas ult, not only late but before they've done anything. Also there's been times I let everyone know I'm gonna be going in on Voice Chat and the second I go in everyone gets the hell out. And the dreadful teammates that do nothing at all to save you when it's clearly possible and those that try to save a surely dead teammate and get themselves killed. Enough of that and on with the actual guide.

To do well in a pubstomp you will at least need a semi-competant team at least given they're at the skill level their PSR says and you're not up against a pubstomp yourself. But you MUST control the game, meaning mid. I know this has been said many times but playing mid is VERY important unless you have someone way above everyone in your game's PSR and somehow made it in there. On to heroes that are good for pubstomping.

[Holy Shit 15 Minute Concede]
Warning: These 2 heroes are both rather situational, and need some sort of basic items to be able to do their job but once they get the first couple of kills with little to no deaths it just gets ridiculous.

Pebbles - Just the sheer amount of ganking he can bring is amazing. Though there are many just as good gankers its also the mind-game of playing against him. Just a huge-ass rock dude that pops out of no where and kills you in less than 2 seconds all the time. It's just painful. More often than not you'll be able to break them so much in the first couple of minutes they'll just give up.

Deadwood - similar concept except he's got teh FALCON PAWNCH.

Thunderbringer - 350 damage nuke that has a bonues 11% hp gone... Owee. And if you just barely get away click R and look for the "FUUUUUUUUUUUUUUUUU" in all chat.
But yeh for him a better much better guide to playing him is found
[Hero] Thunderbringer - Heroes of Newerth Forums

[Very Strong Pubstompers] Generally the safer and more reliable pubstompers.

Arachna - Great ganking with ult and especially at this level they won't carry tp's around which is basically a pretty good counter to you. Also most of the mid heroes are int nukers and your Harden Carapace counters it pretty good. Though you got to be rather careful when ganking as you do need quite a bit of farm to scale. Basically I just lane mid and gank if a lane really needs it other than that I just rice for most of the midgame always having at least 1 tp with me. I buy 2 before leaving base and just go farming popping into teamfights. Also when ganking I like to throw my ult on one person most of the time my team is able to take em out and just start webshotting the other hero as it keeps them from getting away most of the time unless he's a str and you should always go for the int/agi unless the str is low on HP.

Wretched Hag - Ridiculous amount of burst and a built in blink on a ganker! What can't you love about this? You've just got to be very careful with how you blink in as hag's extremely squishy.

Valkyrie - You gotta know how to land those arrow's and you're pretty much fine.

These 4 heroes I find are very good at wrecking pubs. Either breaking their team so much they don't even have any lategame potential or being able to gank very well/control the game but still scale very well.