Watch for high serials. Most inexpensive mod chips/sliders are locked out on high serials and new revisions. I don’t know how you’ll be able to check this without opening it up in the store :P, but do.
If its slim (new hardware, the skinny one), watch for these revisions-
SCPH70xxV12 (most of them are this)
V11 is still fat PS2 (the original) bios and lockout, but its obviously a new hardware. V12 is all new bios and lockout, and you’ll most likely need to buy cards that will work with this. Since this is newer, these cards/chips are more expensive.
Pretty much, the lower the SCPH/Serial is, the cheaper the chip (not necessarily better).
Also: Sodering a PS2 takes balls. I helped my friend soder his with the Magic soder chip. I don’t remember which version it was (3.1/Pro/V). This chip made you go between layers (the fat PS2s are layered PCB), so you pretty much have to take the whole thing apart. And depending on your Serial, you’ll either have to do some lines, or a HOJILLION lines. We did V5. It was fucking nuts. I think it was like 20+ lines, to crazy small points. One of them was right near a SPU chip. Higher than that and you only need to do like 17 or 18 lines, or so i’ve heard.
On the topic of slidecards/swappers: Now, :P, i’ve only ever used one (SwapMagic), on only one type of hardware (SCPH60xxV7=Old hardware revision 7), and <i>it didn’t fucking work</i>. The game i tried to play on it was BeatMania IIDX 8th Style. Now, it could have been because this game needed a special controller, and wasn’t on the standard disc, i dunno. But it didn’t work I was really pissed. Also, it didn’t play backups right. It would play SOME, and not others. I was never able to determine what characteristic about one disc made it work as opposed to the other. =(
However, on my PS1, i used a similar solution (Breaker Pro, which was at EBGames, believe it or not :P) and it worked amazingly well. Its a swapper, meaning you load the disc, then load the game. It worked with all my backups. I never tried an import. I loved it.
Then there are pluggers, but i’ve never used them. =( Can’t tell you much about it aside from the fact it plugs in (like PCI) into the PS2. I don’t even know how the fuck that would work, i can’t think of anywhere that it would go into, aside from USB/IEEE1394, but i know sony restricts alot of their access to the system, :P. Also, i’d imagine this would be version version specific, because i’m sure Sony has locked it out by now.
My XBOX is modded too, (XCuter2.6), so i guess i’ve got experience.The XBOX was a piece of cake compared to the PS2. You can attempt the soder if you want. Sodering isn’t really that hard. =\ If you’ve done it before, you probably have enough skill to do the easy leads. Most chips you buy give you HUGE points on the chip (the XBOX chip’s points were like pennies :P) but the hard part is getting the leads down to the board. On the Xbox it was bad, but i had alot of room to work with (thank god its so big :P). On the PS2, there were alot of leads we let go 'till the end, then we lit candles and prayed before attempting to hit them. Like i said, one of them goes down a board, then right next to a SPU chip :P. I’m only adding this huge paragraph down here because i got carried away, and because of my bad experience with the Slider i purchased. Maybe you’ll get a good one.
So, really-long-post-that-i-got-carried-away-with short:
>Go for low Serial if you want a cheap chip
>Soderless solution failed me, maybe it’ll work for you
>Sodering a PS2 is incredibly insane.
If you have any other questions feel free to ask me, even though this is kind of weird 'cause i originally asked you about chips before i purchased mine