IMHO I prefer use standard disks. Also some Microsoft notes sugges in SAN enviroment (that are similar to virtual enviroment) to use standard disks.
If you use a 1:1 mapping between volume and vmdk you can simple resize the disk (is little more complicated if for version before Vista).
One reason to use dynamic disk could be have a single volume greater that 2 TB.
Andre
Andrew | http://about.me/amauro | http://vinfrastructure.it/ | @Andrea_Mauro