e60's here are notorious for their constant panderings for attention (read: they're service whores) electrical problems and the fact that they have no door protection iirc, so dent easily.
E39 there's a massive following for these days, in the UK they're now the most common 5 as the E34 is dying a slow death. The E34 is now a disposable car that can be picked up for £400 and binned when it comes to MOT time. They're disappearing rapidly.
E39s are doing a roaring trade, especially pre-2001 models who evade the new "green" taxes. Be prepared to have a fight on your hands, the rear E39 suspension is easily as complicated as the floating link E34 suspension and tends to loosen up later in life. If you let them go they eat tyres for breakfast.
There's also been some interesting electrical glitches with the E39 - it's heater 'hedgehog' is prone to failing and flattening the battery, locking you out of the car. (It's called a hedgehog because of the shape of the heatsink on top of the heater resistor) Gearboxes are prone to going pop in the 100-120k miles mark as well. Very common for them to pop up on the uk forums going 'argh gearbox failed!'
Other than that, many think the E39 outhandles an E34 as the E39 was essentially an E34 with floating link rear suspension... the engines are slightly better as well - though more prone to electrical faults and vanos problems. If you buy a straight 6 of either model, get it code read before you buy - they're very prone to exhaust side cam sensor faults that default the vanos unit into a certain position - which then sticks there and the next time it tries to move... it breaks. I'd get it code read at least once every six months as well.
The diesel E39/60s are also prone to having major turbo failure - but I doubt you'll go near one of those
The v8's are where it's at - the E39 535i and 540i manuals are the pick of the bunch with the 4.0 M60 going up to a 4.4 M62 after the first few years of production.
Oh, something I nearly forgot: the early E39 straight 6's were NIKASIL blocks... beware, the odd failure still pops up to this day on the UK forums.
You pays your money and you makes your choices
