All SD cards using Panasonic chipset (such as Panasonic, Hagiwara M-series, etc) have 10 mb/sec data transfer for 256MB & above. For 128MB & below its 2 mb/sec. For SD cards using non-Panasonic chipset, transfer rate is 2 mb/sec for all capacities.
As for how the brand compares, well let's say most brands are quite reliable. However I have heard of Sandisk conking out now & then, so........ Frankly, if speed is an issue, then you have not much choice. Stick to a brand that uses Panasonic chipset such as Panasonic or Hagiwara M-series. If speed is not an issue & you don't mind 2 mb/sec then you have a wider variety of brands to choose from like Twinmos, Transcend, Sandisk, etc.
As for the price, I believe a Panasonic 256MB is somewhere between $160-170. As for Hagiwara M-series, they appear to be quite rare & their distributor's RRP is $150. Keeping in mind different shops have different prices.