The short answer
Neither MyProtein nor Bulk is always cheaper. The better deal changes with discount codes, flavour availability, pack size and whether subscription pricing is active.
The fairest comparison is price per 100g for similar product types, then protein per 100g if the products have different macro profiles.
Where MyProtein can win
MyProtein often has a wide range of flavours and frequent promotions. During stronger discount periods, large Impact Whey packs can become very competitive.
Watch variant pricing carefully. A good headline offer may not apply evenly across every size or flavour.
Where Bulk can win
Bulk can be strong on simple product ranges and larger pack value. Some products also have clear nutrition and serving data that make comparisons straightforward.
As with MyProtein, the best deal depends on the exact product and current promotion, so compare live prices before committing.