Really depends on the car and the price difference. People use Dayco timing belts all the time, and I would use one on my beater. My other car has a timing chain. If I were buying a timing belt kit, I would probably get the Gates. I have no issues with Dayco belts, in fact I do like them, but they idlers and tensioners sometimes bother me (often different from OE fit).
I use Dayco & Gates timing belts interchangeably. In all the ones I've put on, never an issue with them later.
Dayco, Gates & CRP are all OE suppliers to VW for timing belts. I would use any of them with confidence. When I did the timing belt on my Golf, I put on one of the Teflon-coated Dayco belts for S&G.
I've always heard people complain (online) about aftermarket parts store tensioners more than belts. I would use either a Dayco or Gates belt.
If you're going to do TB, tensioner and water pump, if any one of those parts is bad, you have to do it all again, so it makes sense to go with good stuff.
On an interference engine I would prefer manufacturer or OEM brand belts, tensioners and water pumps. Parts store stuff may have a lifetime warranty on the parts but that won't fix the damage a bad part could do.
Dayco is pretty decent, right up there with Gates in the aftermarket world. I got a free t-shirt from Continental because I bought like 5 timing belt kits from them for used cars that weren't Ford brand at work, t-shirt was cool, price was low, and quality was high.
Dayco, Gates, Goodyear cam and ancillary belts - I'd use any of them without a worry.
Gates made all the belts for the Australian built Mitsubishi Magna and 380 models, Gates-Unitta is the supplier for Japanese made Mitsubisis.
Very few reported belt failures on these models, despite the average Australian being too lazy to change his Magna or 380 belt at the recommended 5 years/ 100,000 km.
So Gates woulkd be my choice if I wanted to be 110% sure of no failure.