With competitive rates on no-contract sim only mobile plans. What phones are value for money when we eventually need a new phone?

Tbh, really depends on your needs. Do you want a better quality or better value phone? I've always been an iPhone user and love the simplicity of the iOS. I'll probably be 1 model behind the latest one.

I did however try out the S20+ months after it came out. Samsung, challenger retail price is 1.5k, shopee etc selling at 1-1.1k. I bought it at 900 from carousell. There will be people selling below market rate as they want to make a quick buck by selling off the phones they get from their phone plans. Most likely using a company contract. So I make sure that I get a sealed device with receipt as proof of purchase. Mine was sealed, came with starhub receipt and starhub re-usable bag.

You may pick a device and just Google and find the cheapest available one and buy it.