There are a lot of different things between Steam, 4D1, and TeknoMW3, you have to make your own opinion.
First of all, Steam: you buy the game, there are hackers of course but they are for a lot of them banned after few weeks/month and you can't change your prestige or anything without being sure you won't have to pay your game again because of being banned (I honestly don't believe in undetected hack but I know I should for some of them), but at least, it's the official game with official MAPs etc...
Then, 4D1: you don't need to buy the game here, even if you need to have an original version of MW3 (Downloadable), then you make an account on their website and you can play with actual MW3 steam stuffs (By stuff, I actually mean that the Steam version MAPs are used here).
About hackers here, some wallhackers here, few aimbots there, because they aren't released, so made by people using it themselves, but apparently, nothing is easier to unban yourself on 4D1, either you are account banned, then you wait 5 days or make another account, or you're server banned, but you can use released stuff to unban yourself.
TeknoMW3 finally, blocked at 1.4.3XX version, so you can only play in the original maps of the game, not others like terminal etc (But they are releasing a new launcher/DLCs to allow people to play on these maps.), about hackers, a looooooooooooooooooo[...]oooooooooot of hackers here, there are aimbots, people who can crash your game, crash the servers, WH, people take over the control of server by stealing admin's ID.
But, on Tekno, when a hacker is banned, he is banned in a "sure" way, there are few and hards way to unban yourself from any TeknoMW3 servers.
So, about steam : you have to pay, and not hack to be sure.
And 4D1&Tekno : In a way, hacking is "hard", unbanning yourself is easy, in the other hand, hacking is easy, unbanning yourself is hard, almost impossible.