All of those external models will use one of the three existing OEM 250GB/7200rpm/8MB cache drives, which are made by either Hitachi (formerly IBM), Maxtor, or Western Digital. All 3 have nearly identical wholesale prices, and some makers (such as LaCie) freely swap suppliers.
Of those 3 drives:
- the HGST (Hitachi) is the fastest, quietest at idle, and coolest running. It also makes a disconcerting calibration sound every 10 minutes (described as anything from a cat's meow to a creaky barn door), and an even more disturbing clunking sound every 23.5 hours.
- the Western Digital is nearly as fast. If you end up with a fluid bearing model (which the HGST and Maxtor have as a standard feature), it will be nearly as quiet at idle as the Hitachi. However, there is no way to tell which one you will end up with (WD2500JB-Exxx has ball bearings, WD2500JB-Fxxx has FDB). No calibration sounds, and muted seeks. IMHO this may be the most reliable of those 3 drives.
- the current Maxtor 3 platter IDE design, from what I have heard, has above-average failure rate. On paper it is a decent drive, somewhat slower in real world tests than the other two.
The casing, interface, and warranty are probably more important considerations.
For the casing, I would look for an aluminum one acting as a heatsink for the drive, as opposed to a plastic casing with a small noisy fan, bound to fail in a few years.
For the interface, LaCie is one of the few offering Firewire 800. This won't be of interest unless you have a last-gen Mac or Powerbook, as every PC with built-in Firewire I have seen as FW400. Firewire 400 is faster than USB2.0 (despite the latter's 480Mb/s rating) in real world applications. All the above drives have max sustained transfer rate around ~60MB/s (=480Mb/s + overhead), which will saturate a non-FW800 interface.
Warranty: the OEM drives themselves have a 3 year warranty when sold bare. The external retail versions usually seem to feature a 2 year warranty.
My personal experience with LaCie is that they look best on paper (FW800, slick cases), but skimp where it really counts (2MB buffer on all but the 250GB model, plastic case, small fan, 'sandwiched' 2x250GB 500GB model with lousy cooling...)