I have the same film scanner. Exactly how is the quality worse? Grainy?
Blurry? Colors off?

I have either the same scaner or one close to it, I hav the Minolta
Dimage Scan Dual III.

There seems to be a lot of disagreement on what is better to scan,
slides or negatives.  What I find is that slides are easier to scan and
take less adjustment with things like exposure settings but that that
if I take the time I get better scans with negatives.  I also seem to
have a lot of scratches on my negatives but not so much on my slides so
this makes scanning the slides easier.

I know some slides have scanned much better then others and I have some
slide scans that I am not too unhappy with, this one I kind of like
http://www.sewcon.com/photos/UL%200603.jpg

But even here you will note a very limited range, the highlights are
blown out and there is zero detail in the shadows, for this photo that
does not matter all that much.

Here is a photo that I would have had a hard time with slide film but
not too bad with negative film
http://www.sewcon.com/photos/0502.jpg

I shot a lot of slide film when I was younger, I wanted to view the
photo large but did not want to pay for large prints. I more to more
print film as I got older.   In general I like my scans from negative
much more then those from slides.

I know that many other much prefer to scan slides.

Is it posible for you to post an example of what you think of as a bad
scan from a slide?

Scott

So what films is he using?