The main difference between LC tank based VCO and inverter chain ring VCO is that with the first one you'll get ALOT cleaner output (as mentioned above phase noise performance will be better by far) but it will be harder to achive 600 - 1200 MHz tuning range. On the other side chain inverter ring VCO will get you that range easly, but phase noise could be a problem. Try to find out what max phase noise your desing can have, and on this base your choice.
diffucult to achive tt range ..but you can try ring oscillator with diff. delay cell control the current replica biasing ...but trade off power consumption is high n phase noise..