We are leaving next Saturday on the Monarch flight and this has crossed our minds too.
We used to like the First Choice flight because it left Gatwick earlier and arrived earlier in Goa and we didn't have problems with crowding, but unfortunately, they no longer go to our favourite hotel.
I remember a few years ago (when we flew with Monarch) another charter flight arrived at the same time and we had to wait a while to get off and when we did, we had to wait by the side of the aeroplane while another plane was moving away from the terminal (I got sunburned). When we got inside the whole arrivals area was awash with people and it took two hours to get through Immigration. Once through we still had to wait for our luggage and even then we didn't know which carousel it would appear on. As we had arrived already feeling tired and crumpled, by the time we left the airport, we felt more tired and crumpled.
We have noticed, however, that over the years the process of getting through the airport has got faster as they have more immigration desks. What is annoying though is when you have people who have either not filled in their immigration forms or filled them in and left questions unanswered so hold up the line. They are nearly always in front of me!
What about on the way back, and having to stand outside the terminal in the sun waiting to get into the terminal; but I guess I will just have to wear a big hat! Once inside you can wait ages to get through immigration and the queue can get mingled in with those queueing to check in. What we have done in the last few years is to check in and then get a cup of tea in the little restaurant then go through immigration.