Whichever option, do start very early (say 4 am) to reach at lunch time, I think there is some work going at Khambatki ghat and your aim should be to reach exit of NH4 as early as possible and then give around 3-5 hours to reach Goa (depending upon exit point).
1) Chorla route is a good option considering it is a scenic route and road quality is lot better but with disadvantages such as being stuffed with trucks, buses particularly in narrow patches. Remember to fill up fuel before leaving Belgaum.
One more drawback is one has to go through Belgaum traffic particularly if you miss left tun to touch the "ring road" (or bypass road don't remember what it is called).
Still as I said, depending upon the place where you want to go in Goa (e.g., Ponda, Sanqelim, Amona, Marcel etc) this will be a good option.
This should be around 3-4 hrs after existing NH4.
2) Amboli route is standard choice and in my opinion the safest option when not raining. Though it is patchy once you leave NH4 and till the time joining NH17. I have heard the potholes are filled / being filled but not sure abt the status. This route is particularly preferable when one wants to go to Pernem or even Mapusa.
I had also taken Kumbharli ghat route (after Satara) once but wouldn't recommend in this case. There is Amba route option too but not sure about road conditions and will anyway be crowded.
This route could take around 4-5 hrs after existing NH4.
Just for completeness, I would also add Kolhapur - Gagan Bawda (karul Ghat) route which last time I visited was BADLY pot holed (4 years back) and I was told it has mostly been like that. But the ghat itself is scenic and different - "spread out" - compared to other ghats. Btw
, can anybody comment on Khanapur (NH4A) option? I think that will be shortest route but last time I drove (3 yrs back) it was the WORST route (this route allows us to stay on NH4 for maximum distance!).