My friend owns the ashdown and I've used it many times. It sounded great at first, but after about a year of light use it sounded horribly muddy (I don't know what broke, but something did!) and the DI now just produces a steady 50hz hum, instead of a bass signal.
Out of those 4 I wouldn't touch the Behringer with a 10ft pole, (out of personal experience, I'm not flaming!), I wouldn't reccomend that particular Ashdown, so that leaves the SWR or the Warwick.
I love the sound of Warwick amps, and I gig regularly with a 150w amp (it's plenty loud!). So my money's on the Warwick, as you'll probably get the best tone and flexibility with the lowest price.
EDIT: IIRC Behringer rate the power of their amps by peak wattage, not RMS. This means that the Ultrabass you've linked to will be closer to 150w RMS, therefore a similar volume to the Warwick.