Among the vehicles you’ve mentioned most of them are famous for NOT being economical and hard to sell. Since it’s your first vehicle, better to go for a reliable vehicle like Corolla 141. I know about the old a33 Cefiro and the newer version might be better.There are only a few number of them around here, so I’ve never met an owner so far. Mark X would be a nice car to drive with loads of options and uncommon looks but with low fuel economy. If fuel is not a concern for you, go for a Mark X eyes closed. There will be some repairs (considering the age) and most of them would be running repairs. Also the finding the parts will be a bit of an issue. G11 is also a comfy ride but being large saloon with a 1.5L fuel economy is not so good.
Since it’s your first car, go for a famous and reliable model with service records. Also make sure to take someone who has a good knowledge about vehicles in order to check whether the car had been met with an accident or to check the mechanical condition. Don’t be hesitant to pay a bit more if the car is in perfect condition with records and trust. My advice is better to go with a car like Corolla 141 or Premio 240(Most of them are used like hell,so less number of good examples are available). Fd1 and Fd4 are also good cars with good reliability. Best thing is to go and check those cars. Make sure to do a test run. Also refer to the thread in the General Automotive section “How to buy a used car in Sri Lanka”. Good Luck!