I like to use oval head screws and use a countersink bit in the siderail to get them nice and smooth. agree with tscottn on the fill the holes and redrill.
screws - https://smile.amazon.com/dp/B075DH4MFQ/
countersink - https://smile.amazon.com/gp/product/B00947BNFG/
you can find the screws with different drive types, I have square drive ones and have seen slotted as well.