Phase Noise id principally dominated by Quality Factor of the Tank Circuit in MW Oscillators regarding to Linear Phase Noise approximation of Leeson.There are obviously other noise related parameters such as NF, Flicker Noise corner frequency,Voltage Swing,OP Current etc. but Q factor is essentially dominant.
An accurate and robust optimization technique has been derived and explained in Ulrich Rohde's book.Its' mathematics are pretty cumbersome but it's also important to able to understand of the mechanics of the Phase Noise.
Ulrich Rohde ( and surely Randall Rhea ) is the guru of the oscillators and you can find lot information at **broken link removed**.
I suggest FETs that used in LNA designs. For example, ne3514s02 or better.
Must have high gain in required frequency point, because need to make weak coupling. S21 must be enough, to go through weak coupled resonator. There are many papers suggest push-push oscillator or weak coupling for low noise. Microwave absorber above oscillator is frequently suggested, there can be some unwanted RF paths between oscillator and enclosure. Also you can protect oscillator from vibrations with some special "soft" mounting of PCB inside enclosure. Vibrations can modulate frequency that goes through dielectric resonators, diodes or even transistors. Observed by knocking CW oscillator enclosure with screwdriver or by directing very loud music to it.