Default [Q]Unbranding my phone

Hi there,

I'm the proud owner of a Dutch T-mobile branded HTC One M8, can some one please help me how to unbrand this phone, what are my options?
- HTC Dev? --> if so, wich rom do i need to install to get the most clean version of HTC firmware on my phone *with Sense
- Rooting? --> if so, install a custom rom?
- S-OFF??

Thanks in advance!

Sam
Phone: HTC Touch Diamond
PC: EVGA nForce 780i, Q6600, 4GB, 2x 8800GTS 512, 1750 GB HDD, Coolermaster Cosmos 1000, 620W