I've seen quite a few good second hand offers for PS3s, Im sure I saw one for a 320GB HD for under £200, which seemed quite good to me.
I'm assuming if they offer 320GB, that like the 360 you can burn the games to disc? Or is this all purely download space?
Also, what would the risks (bar the obvious, warranty, etc) be with getting a secondhand PS3? I personally had a [censored]ing nightmare when I bought a secondhand 360, but Im a little hopeful with the PS3 since it appears to have far less problems in terms of hardware.
Any particular model I should avoid/go for? Any advantage to slim bar the size?
A fair amount of PS3 games have mandatory installs, so yeah, you'll be needing that space.
I'm not too sure what the status on opting to install any other game is, though. I'd presume they'd have added it by now if it wasn't already there before, at least.
Second-hand PS3s could suffer heavily on the blu-ray side of things if the drive wasn't kept in good condition, but you can probably clean that up yourself at least. Other than that, it's the same as any other piece of electronics: wear, tear and an unknown level of care will impact on how long it lasts in your hands after another's.
Slim is smaller, quieter and will probably stand up to much more than a PS3 that could be as much as 5 years old already, given that they've only been on the market for 2. Given that the original PS3 model looks like a hideous tank of a machine, I'd recommend the Slim for sure. But, aside from the [censored]ery of Sony slowly taking away ports and features (like backwards compatibility) from the PS3 throughout its life, there's not too much between the Slim and the immediate version of the original hardware that preceeded it.
If you go right back to the launch PS3s, you can get some on-hardware backwards compatibility, but you'll never really be able to identify that before purchase.
It's definitely a lot messier to buy a used PS3 than a used 360 (aside from ideally avoiding any 360s from before 2009), but if you can get a Slim at a decent price, you might as well.
I'm hoping to pick up a PS3 Slim myself at some point later this year. Once I've built up enough of a stable cash flow. It's still, unequivocally, the best Blu-Ray player you're gonna find on the market. Not least because Sony holds back updates to OEMs...
I say go for it. I've only ever bought pre-owned consoles (with the one exception being, strangely, the PS3) and I've had few problems. One broken PS2 and a Mega CD and that's it, but the PS2 lasted years before it broke.
However, there are risks, so I'd highly recommend getting it from CeX or GameStation or somewhere that gives you a guarantee on its pre-owned goods, just in case.
As for advantages for the slim, it's... smaller. That's about it. If you get hold of one of the first batches of PS3s from 5 years ago, you'll be able to play about 4 PS2 games on it, and if you buy one that hasn't connected to the internet in a couple of years, you can run Linux on it and pirate the [censored] out of it. That's about it. Oh, and there's a slight possibility that if you get a really old one, it will come with a SixAxis instead of a DualShock, so no rumble for you.
Although, oddly, if space is an issue (as you've mentioned it is when talking about your 360), there is no option to stand the slim up, whereas there is with the old-school one.
But no, the only major differences will be HDD sizes. To be honest, as Slims have been out for a while you'll probably end up with one, and I'd have to say that the smallest HDD you can get is 120GB and you won't need more than that. There's so much space there that I abuse it.
Not all games have mandatory installs and, to confirm, yes, most games do give you an install option also. It's an option you'll want to use because you really do have that much space. I only have a 60GB 360 and have downloaded more DLC, installed more games and stuff on that than I have on the PS3 and still haven't filled that up.
I abuse my space on my 120GB PS3. Gave PlayStation Home the full 12GB install even though I don't use it because I can. Still got tons left.
Like, if it's a good deal, get a bigger one, but don't shell out extra money on a 160, 250 or 320GB over a 120 because there's really no need. Unless you obsessively download HD movies, which there's not even any need to do as it's a Blu-Ray player.