Both Access Virus TI and Alchemy are great products.
If you have the budget, get the Virus TI Desktop or Snow TI (low budget). Purchase Alchemy in the later stage. Then you have both to work with.
Btw, Sylenth1 is a good purchase as well. I use it frequently combi with TI sounds. I use Alchemy for Pads and some synths.
Cheers