There are a ton of threads about this. But I'm not sure of your actual question. Are you asking which is easier to scan, negative or slide? If so, slide film doesn't require as much color correction, but can be very difficult to get the full range of darks to lights in a scan. A lot depends on which scanner you're using and what software settings you're using. A scanner with a high DMax and multipass will make getting the most out of your shadows without blowing out your highlights easier. Color negative film is usually much easier to scan, but much more difficult to color correct. Again, this depends on what scanner and software you are using, as some will do some color correction automatically. But to get the best color correction, you're going to need to do it by hand. No automatic software does a great job, though many do a good enough job (for most people).
In any case, learning to scan film well will take some time and patience. I honestly don't have a preference when it comes to scanning. They both are about equally difficult to work with. Black and white film is usually a lot easier to scan and process. How well either will scan will have a lot to do with the scanning equipment you use (I prefer a DSLR for small format), your technique (with both the scanner and software), and how well the image was exposed and developed to begin with. Plus certain films, like Velvia 50, are notoriously difficult to scan (though definitely not impossible).
