The faffiness of velcro straps depends on what the rack's like: If you've got to pass the strap between the tube of the rack and a mud-deflection plate, it can be quite fiddly (especially if the bike's against a wall), whereas if there's loads of room between the rack and the wheel so you can easily get your hand in underneath it's quite straightforward.
Either way, it's not QR like the Topeak or Racktime racks, where you just push a button and slide them in/out. More glove-friendly.
I like the Super-C because it's no-nonsense (no zips to go wrong when you cram it full of unexpectedly unwanted layers), waterproof and it should last for ages. I dislike that it's basically one big compartment for your lock to bounce up and down on your lunch in when lightly loaded.
I like the Arkel Tailrider because it has lots of little pockets for keeping tools and things organised, and because it doesn't look like an out-of-place shoebox on a 'fast' bike. I dislike the low capacity and shower-cap waterproofing.
I like the Carradice Prima because it's a good compromise between volume and pockets. It isn't waterproof, and has now been discontinued. I've re-velcroed mine once, and am wondering if the zips will last long enough to re-velcro it again.
I had one of those ugly Carradura expanding-wedge bags for a bit. The zips failed. You get what you pay for.
I reckon there's a strong argument for avoiding zips, especially if it's getting daily use. So either a roll closure or drawstring+flap.
