Beer made from kits varies a lot in quality. For lagers, if you just use the standard yeast, Coopers range of lagers are good. They use their own yeast strain, dried for them by Maori. No other beer kit out there contains that strain.
It is generally a very decent strain for lagers, unfortunately they use it across the range and it isn't equally good on the ales.
Muntons use S33 from LeSaffre for their "Standard" kits. This is actually a baking yeast strain which is rebranded as brewing yeast. It works well, never any problems, but it does produce beers that all taste alike because of its rather brutal fermentation. For their Premium Kits, they use SO4 instead, a very good strain particularly for promoting fruitiness.
For really good quality beer kits, it is unfortunately often necessary to exchange the yeast for something else, Nottingham, SO4 etc.
John Bull