Farnell and CPC are worst in terms of the website going down completely, either the "access denied" thing, simply not loading, or for maintenance. Farnell also seems significantly less reliable than RS in terms of getting stuff delivered next day - they always seem to use UPS who are absolutely awful (most RS stuff gets to me by royal mail by ~midday, vs late afternoon or a day late for UPS). And yeah, CPC tends to completely ignore ESD - if I buy expensive parts half the time I end up emailing them for a refund due to no ESD packaging, but they never seem to learn (at least I get to keep the parts though - OK for hobby projects as long as they still work!). CPC also managed to associate my private account with my employer (who I used as a delivery address a few times), and started issuing my refunds to them!
RS on the other hand used to just drop me back to the main page regularly - I think it's improved now but also slow. And so many simple things are in huge pack sizes, at least put a bloody quantity selection or a total price _including_ minimum order quantity sort thing so I don't need to get past the 100 reels with low unit prices to find the 2 pack that I actually need. This goes for Farnell too, though they seem less bad at it.
As for Digikey, I often use it simply for parametric search to find a part, then check with local suppliers if I'm not going to meet their minimum order quantity. They are kinda expensive sometimes but assuming I meet minimum order size for free shipping I feel I get more for the money than with RS/Farnell simply because the good website saves me so much time and anguish.