I can't say anything about the Three Coasts, so I haven't voted.
I have completed the Border Raid 600 once, and packed it once. The route changed between the two but that wasn't the reason for packing. The weather was, combined with hanging around too much on the first day, meaning not much sleep or time in hand when the weather turned really nasty. (Driving rain, and 65mph gusts of headwind).
It's a nice route (or the 450km or so I did was, anyway). It's much less hilly than the likes of the Bryan Chapman, without involving tedious mile after mile of pan flat terrain, which gets old very quickly. The old version of the route, which is similar terrain wise, was the first 600 I completed.
Although it's X-rated, there are opportunities to get a sleep stop at motorway services on the M74 (Annandale Water, iirc), at around 350km, or a bit later at Carlisle, if you think you want that.
The route sheet uses symbols rather than the traditional L @ T etc. Personally I don't like this, I find the symbols much harder to interpret. I've transcribed it to gpx if that would be helpful to anyone.
I have been thinking about entering it again this year.