If I spend $500 or less every month, should I opt for a miles or cashback credit card?

If its me, I will prefer cashback as my spending is below $500 per month.

This allow me to have more consistent rewards, rather than miles that I need to accumulate over a long period of time for a decent redemption.

I will still keep a miles card for large spending.

For big ticket item, such as for travel, wedding, home furnishing etc, then I will use that miles card to earn miles.​​​

UOB One, min spend $500/month - 3.33%

$500 x 3.33% = $16.65

$16.65 x 12 = $199.80

Miles cards at 4mpd, no min spend

$500 x 4mpd = 2,000 miles

2,000 miles x 12 = 24,000 miles

That's a one-way Business Class ticket to Bangkok ($962).

But it's Bangkok.. I can fly Scoot...

Well, using the right card and you can fly Business Class with the same spend.

Travel better for less.​​​

Certainly cashback card would be a better option because you can see the cashback rewards and use it after just a few spend.

For miles card, you do have to spend quite a lot to clock a good number of miles.

Depends on what do you want out of your spendings. It also depends on your spending pattern too. If you're not even a traveller, I would suggest you don't even bother with miles. Personally I would think that cashback may work out better for you because the credit cards that give high mpd have expiry to the miles (which means you probably should clock sufficient spending in order for the miles to translate into something valuable), the credit cards that have no expiry to the miles have low mpd. So unless you are fine with taking a long time to accumulate your miles, it is more likely that a cashback card gives you a more tangible return.