I have used both sugars and malt extracts to brew pre-hopped canned kits, I assume this is not the type of brew you are making as you mention a boil.
With the sugars the beer turned out ok but the best way to describe it is as a little 'thin', one of my friends described it as being very watery, of course it still has plenty of alcohol.
Once I tried using dry malt extract instead of sugars there was a noticable difference to the quality, it felt fuller, had alot more body and just tasted alot closer to a 'real' beer.
I would not advise anyone to use sugars rather than malt in there brewing, the price difference is pretty small considering the difference in quality I experienced.
Hope that helps a little!