I would say do it weekly. Here's why:

Exchange fees will probably be a big incentive for you to buy weekly instead of daily. It really depends on the specifics of where you're buying, as some charge a fixed fee for every time you deposit/buy. This also applies to withdrawal to your own wallet, you want to minimize those fees as well, so you might do a withdrawal once a month for example.

Another factor that might push you towards weekly buys is the mental one. If you still have fiat around and you see the price going down you might get anxious waiting for the next day to buy more. Once you already allocated the weekly payments, then it's done so no reason to keep thinking about the price for the week.

Because there's no way of knowing if daily or weekly will get you more bitcoin per fiat unit, I reckon it's better to just minimize exchange fees and keep your head clear of price thoughts on the week.