I'm not a stock photographer by any means, but I love both color negs and slides. In my experience, color negs are a lot easier to shoot, but color slides are far easier to scan/color correct/etc. Both look great, so I see no reason why it should be a huge issue for you. Personally, I find Ektar to be hit or miss and really like the roll of Fuji Reala that I've shot. Give that one a try next just for comparison's sake.
latest Kodak reincarnation of the color neg has been optimized for scanning, or you can use Rollei with a transparent base, IMHO negative gives you much more room to work with than transparency
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