My T42 has passed to mums household, running XP for occasional needs.
At home is a T410, Windows 7, running nicely. Oh and and a 2nd on under the TV as an entertainment hub.
Typing this on the work W520.
Among the desirable attributes are FIXABILITY.
What other brand has numbered or illustrated screw holes on the underside to remind you which screw loosens which item? Or a keyboard that pops off with 3 mins work?
Over the years I've replaced various parts - drives, keyboards, it's the fix ability (parts off Ebay) I like.
And the stream of ex-corp ones that will arrive later that can be bought for home use.
Experience of office colleagues has regrettably been that the W5x series is nowhere near as reliable as the T series, overheating and motherboard failure being typical.