Zoom or prime lenses?
This is a long debate and strongly depends on the wishes that the photographer has; thick books have been written about this.
From a design and manufacturing point of view a prime lens will be better in terms of contrast and sharpness than a zoom lens, although the difference with new design and manufacturing technologies is getting smaller and smaller.
Having said this there is an enormous difference between the various quality prime lenses, e.g. there are awfully good prime lenses (like the 100 mm AF Macro Minolta) and quite poor lenses like some of the b-rated brands are according to the tests.
The same holds for the zoom lenses.
I agree with Fritz that the 100-300 mm APO (and the 100-400 mm APO) from Minolta are quite good, but there are more good zoom lenses (like the all glass 35-70mm AF and 28-135 mm AF (weighing 650 grammes) Minolta of the first generation (introduced in 1984 and replaced for partly plastic lenses in 1990). So before you make a choice, define what you want: many kg's for a number of prime lenses or one zoom lens covering the whole range.
In many tests the Tamron 28-200mm zoom is tested as good, medium quality, not so bad at all (whatever description you want to use. But for this zoom range the limitations are significant (low opening, distortion in the corners, vignetting)
In addition the color rendition of the lenses differ significantly by brand. Personally I like the color rendition of the Minolta lenses. I have many high quality Minolta prime lenses (up to the f4/600 mm) and some zooms (35-200mm, 35-70 mm, 24-85 and 100-300 APO).
For prints of 10-15 cm2, the difference between the best prime (AF 4,5/400 mm and the most modest zoom I have (the 35-200 mm AF is not very large (but of course visible).
I hope this puts things into perspective. If you want to know about the quality of the lenses before you buy, take a look in a good Photo magazine, like the German Magaine Color Photo that publishes an overview of the best current lenses every month.