Rose2boys, I personally would recommend your going exclusively with metal hex dumbbells, for the following reason:
A smart and easy way to keep upping your dumbbell weightloads is to purchase PlateMates, magnetized attachments to the ends of your hex dumbbell that come in sets of 5/8-lb each (for a total of 1.25 lbs per dumbbell) and 1.25 lbs each (for a total of 2.5 lbs per dumbbell). Many lifters, myself included, cannot or prefer not to go from, say, 5 lbs to 8 lbs, or 12 lbs to 15 lbs each per dumbbell because the neither the working muscles, the supporting muscles or their associated joints are ready for that much of an increase. With PlateMates (found on several online catalogs specializing in sophisticated training equipment) you can incrementally increase the weight and thus your strength manageable and safely. PlateMates, however, do not work on rubber or vinyl/Neoprene-covered dumbbells.
So, my rec is to invest in metal hex dumbbells AND sets of PlateMates in the above increments. If continual strength-building is your long-term goal you will have to get heavier dumbbells at some point, but these little gizmos are a wise investment.
JMHO -
A-Jock