I think it really depends on the size and functionality you want. Here are my thoughts.
If you want something 18L or larger you'll have to go with Carradice, Zimbale Sackville or maybe Origin8
Nigel Smythe - to expensive and too posh
Sackville - also from Rivendell, cheaper than Smythe, but still not cheap and I just don't like the design
Zugster - nice bags and colourful, expensive, but I didn't know they made a saddlebag.
Zimbale - Look to be nicely made, they have more features than the Carradice and are more expensive.
Minnehaha - small and look to be lacking in features, like side pockets.
Acorn - again looks ok as small/medium capacity, quality is good, but the leather straps are a bit thick for easy use.
Origin8 Classique - looks interesting, cheap, made from 600D nylon...I wonder what it weighs, dimensions are the same as a Nelson, but I don't think it has a longflap
For me the Carradice and the Zimbale are the sand outs and you can get a carradice nelson Longflap from
www.wiggle.co.uk for $77.