I mean, I'm no expert on computers, but I feel like these are more than enough to run LoL and TF2. You honestly could probably get a machine that runs both these games (with some settings turned down, most likely) for like half the price. I'm on a 2009 MacBook, an Intel Core 2 Duo machine and I can run both games well enough (Mac's aren't even gaming computers and I can run these games).
Laptop vs. Desktop, if you need portability, buy a laptop. Desktops usually offer more power for less, but they're less portable. They are more customizable, though; it's harder to modify or build your own laptop, where you can add extras or upgrade parts of a desktop much easier. Honestly I'm sort of in favor of a desktop/tablet setup, tablet for portable tasks that don't need much power, though the new Microsoft Surface tablets are looking pretty dang powerful, not sure but I feel like you could run LoL on them (with reduced settings)
At first glance all I can tell that's different between the two computers you listed is that the cheaper one has a bit less RAM (8GB vs 12GB), which means that you won't be able to run as many programs concurrently (more or less), but that's hardly an issue imo (8GB is plenty for virtually anything). Both of them look identical (the cheaper one actually has a newer CPU I think, though at slightly lower speed. I don't think it matters much though, i7 processors are insanely powerful, and I think the newer models are better even if they clock in at a bit lower speed; they have newer tech that makes them run more efficiently than the old processors, I think, which I would prefer to a bit of extra RAM. You can always buy extra RAM, assuming your computer can handle it, but buying a new CPU is much more difficult since it's soldered to the motherboard).
A question for everyone else: What do you think about ibuypower? I see a lot of computers on their site for fairly cheap, and the customization is nice, but I don't know about quality, etc.