There are several different aspects of this question. I would say slide film scans "easier", but not necessarily "better". There is unquestionably less grain in most slide film (I mainly shoot Provia 100F for slide and can't see anything like grain at 2400 ppi on a flatbed). It's also easy to get colour balance close to what you want right off the scanner with slide film. Several have commented that you have the slide right there as a colour reference. That's true, but then the colour on the slide might not be the target you seek. For example, you may have shot daylight slide film in shade without colour correction filters on the camera and there will be a blue-green cast to the image on the slide. So generally speaking, the colour balance right off the scan is 'close', but not necessarily perfect without some tweaking later in Photoshop. The high output dynamic range (density) of a slide is nice in that grain is minimized (you won't be adding contrast in Photoshop later), but then there could be more noise in the deep shadows with cheap scanners, and there may be a loss of detail in the shadows and/or highlights due to the initial exposure if the scene was too contrasty for the film in the first place. For this last reason, I generally don't shoot slide film anymore in bright sun. I consider it a specialty media for colourful flowers in shade. And to be perfectly frank, I also shoot slide film for the personal "wow" factor when I get the slides back and hold them up to the light.
Colour negative films are more difficult to scan, as the colour balance right off the scanner can be all over the place depending on the scanner's software and how it deals with the mask, but even cheap scanners can be easily set up to capture all the information, and then you can tweak the colour and contrast later in Photoshop. I tried Ektar, and the grain is incredibly small, almost as good as Provia, but I admit it's hard to tweak the colour later. Reds go incredibly saturated and may be hard to tone down, while shadows go blue, which is really there, but the film emphasizes it. For this reason, I like Portra 160 as my all around film for most subjects. The grain is pretty small, and I usually can get the colours right just be playing with the black and white points of each colour in Photoshop after scanning, without even shaping the curves. I even have made some fairly contrasty and punchy coloured images with Portra by using Photoshop. The negative has all the information. I may not end up with an image looking much like the traditional analogue print from Portra, but as an analogue "raw" format you can work with, it's hard to beat Portra.
I once tried the same flower macro with Provia 100F and then again with Portra. It was possible (with some difficulty) to manipulate them to look about the same.
