Those are two entirely different bats, intended for two different types of hitters. The rocketech is an end loaded bat and -9 oz. The synergy is more of a balanced bat and -10 oz. The rocketech is good for the very strong hitter that can get the bat moving quickly. The synergy is the for the hitter looking needing a lighter bat with length.
I have a couple girls that use the new synergy (gold with clear finish) it is seems to sting the ball pretty well. Of course, the rocketech speaks for itself - I have always liked the response from them but you need to be a strong swinger to get the benefit of the end loaded bat.
IMO - you can't go wrong with either - but I would recommend the synergy from the standpoint that you get an extra inch of bat for the same weight.
Now - Combat Virus - nice bat. Seems to sting the ball all the time.
It's not uncommon for the rocketech to actually weigh a couple of more ounces than what they say, so keep that in mind. That can be quite a load for some players. I would recommend a balanced bat for younger players, unless they are naturally big and strong and have good bat speed and mechanics. A player on my DD's team has been swinging the Anderson for a couple of years. She's smaller than most, but when she does get a solid hit it goes far. Usually I can see her bat drop and she doesn't really make solid contact.
The point about RTs weighing a little more is true - they are actually about -7s. In fairness, a lot of bats weigh a little more than advertised. Anderson maintains much of this weight is in the knob, which is steel. Although the RT knob is smaller than normal, because it is steel it weighs more, and weight "outside" the hands doesn't much effect bat peed (same principle as choking up).
I really think that Mark is right here. In fact, my observation - pretty well honed - is that one of the reasons the RT works as well as it does for as many hitters as it does is that it is SO heavy it force hitters to maintain connection to get it around. In other words, to "connect" the hands and arms to the torso so that the core muscles of the body are doing the work. NOT the arms.
An important concept for ALL hitters, EPECIALLY female hitters. Who at the higher levels of the game use bats that are pretty heavy, relative to their arm strength. You see a lot of 26oz / 27oz bats in college FP. And the girls who swing them by-and-large bench-press less than 100 lbs, and use the bats to hit a ball which weighs 40% more than a baseball.
MALE college hitters swing bats that are about 32-33oz, or maybe 20% heavier than their female peers. Yet they bench press 250 - 300% as much.
Anyway, the RT is a good bat. And the company's customer service is absolutely unrivaled.
I personally like the Synergy better, but I know lots of people like RT's. They ARE very different bats as others have mentioned. It's always best to go with whichever one a batter feels most comfortable with because those bats are likely to feel very different to a batter.
I've hit just about every Fastpitch bat worth swinging. The Rocketthech is hands down the best fastpitch bat available. It actually gets better the more you use it. The sound it makes when you hit hard with is is beautiful. The harder you hit, the better it works. It's fantastic. The Demarini Phenix is #2 in my book. Then the Miken Halo Lite.