I'm a massive nerd, so I've thought about this before. I'd probably say Auto-Leptokinesis. It's basically shapeshifting except without so many, and you could reshape your own molecular structure instead of just having control over your general shape and materials.

Here's my world domination "research and space exploration" strategy. :)

1. Create a high performance computer using blueprints from the internet, or just clone mine, then split it off into a different entity and have it simulate what would happen using different materials and structures to improve its own hardware. Since it has the ability to use real matter it shouldn't need to do as much work as it would simulating everything. It would just need to observe.
2. Have it upgrade itself using that information, increasing its performance and the rate it can research things, and decreasing its size, energy usage and heat output.
3. When it's sufficiently advanced, let it solve problems like faster than light travel, along with researching heat management, energy storage, energy generation, faster than light communication and energy shielding if it's possible.
4. Have it absorb matter from somewhere and turn into a spacecraft capable of faster than light travel.
5. Stay on Earth and send it to another star system to explore and have it create copies using materials it finds on other planets, and have them form a network so they can send information to each other and back to me.

Optional choices:

1. Put the information on the internet for anyone to use, or give it to companies for free, and find a way to make everyone know about it. Hopefully everyone would develop at the same rate and no one would start killing each other or invading countries... Doesn't seem so likely though.
2. Enslave humanity. Self explanatory. Not sure why I'd do that if I could just create another species on a different planet and torture them instead, and that doesn't really seem like a good option anyway.
3. Leave Earth and move to a quiet corner of the Galaxy to create an empire of mantis people. Just like Cave Johnson would have wanted it.

Pretty sure that would end up going wrong since there would be so many opportunities for it not to. The other entity would probably end up self aware somewhere down the line, but hopefully I could find a way to prevent them from enslaving/killing humanity, maybe by giving them no reason to turn on me and staying on their good side, or maybe by just threatening them with the fact that since they came from me and we had the same research we'd be equals and neither could ever win.

Holy shit that was long.

As I said before. Massive. Nerd. :P