Assuming the taxi uses a legit meter, the taxi will always be cheaper than Grab. While it's true that many taxis will not turn on the meter, Grab has the disadvantage of drivers not showing up after confirming their rides if traffic is very bad. And they won't cancel bc then they will be charged a penalty. So they will message you to say they have to eat lunch/dinner, etc. and wait for you to cancel and so you incur the penalty.

One Grab driver scam to be aware of is that the driver will often (maybe 50% of the time) ask you to pay the tollway charge when the Grab trip routing has already factored the tollway toll into the rate. Of course, you won't know that until after the ride is over, since the routing might be next to the tollway, but not on it. You can get reimbursed for the 35-45p double toll by complaining to Grab afterwards, but it's a hassle and you're left feeling the driver was a scammer.

Grab cars are nicer than most all taxis and the drivers have a reason to be courteous, and your destination will be clear. I don't mind paying a little extra for Grab, esp. since I can use a credit card to pay, but for rides when traffic is very bad, I prefer a taxi so I don't have to wait for Grab. During rush hour on a Friday night, for example, it can be very difficult getting a Grab driver to accept in certain busy areas. If you're staying at the GH BGC for a few days, you can check how busy it is for the hour you want to catch a Grab to the airport at certain hours days before you actually need to go. Busy times are 11:30-1:00 pm and 4:30-6:30 pm usually. Also, I can't hail a Grab if I don't have internet (like at the airport) or if I checked out of the hotel hours before.