01-28-2009,07:55 AM
Well,... I hope you find a version, which is compatible with FMCB (~95% of all PS2-Models...).
If you get a 90k with old date-code/8b, you´ll have a brand new PS2 + it is compatible with FMCB. 
Back to your main-questions:
A Mod-chip is preferred in all cases, but the swap-method is easy on slims.
If you already have an original PS2-Disc, then there is maybe a way to create a custom swap-disc.
What is cheapest (from cheap, to more expensive):
-FMCB + ESR
-Swap-Discs
-Modchip
What is prefered (for Backups):
-Modchip
-FMCB + ESR
-Swap-Discs
What is best (for Homebrew and Backups):
Modchip + FMCB, if compatible.
PS2 V7/DMS3 V2 (FW:2.4b7); Seagate Baracuda 200GB
PS2 V7/CC1.0 (FW:34 hacked v2 BM:2.1.6); Maxtor DiamondMAX9 PLUS 160GB
PS2 SCPH-30004R; NoMod+NoLaser
3xSony BBA
3xSony MC 8MB
MAX/Datel 16MB with Boot-CD
MAX/Datel 32MB&64MB
Custom FMCB 1.8b+ Beta-Build, my AIO 0.5, Sony&xRhino-Linux