you want the widest availability and a maker that publishes a single model-level shingled list you can check in one place.
you want a conventionally-recorded 7200rpm drive at 1TB to 3TB, where the P300's DT01-A mechanism is the conventional half of that range.
These two lines occupy the same position, mainstream desktop storage, and both contain a mixture of conventional and shingled models. The good news is that both manufacturers publish which, so this is a question with a documented answer rather than a guess.
Western Digital publishes a client SMR list naming its shingled models: at 3.5 inches that is the 2TB WD20EZAZ and the 6TB WD60EZAZ in the Blue line, with the document stating all other capacity points use conventional recording.
Toshiba's split is by mechanism. The P300 at 1TB, 2TB and 3TB uses the DT01-A series at 7200rpm and is conventionally recorded. At 4TB and 6TB it uses the DT02 series at 5400rpm, which Toshiba's own product overview states is drive-managed shingled recording, and Toshiba names the retail HDWD240 and HDWD260 in its SMR statement.
So the maps differ: WD is conventional at 1TB and 4TB and shingled at 2TB and 6TB, while Toshiba is conventional at 1TB to 3TB and shingled at 4TB and 6TB.
At 1TB both are conventional, the WD10EZEX and the DT01ACA100, and both are 7200rpm. This is a genuine tie decided by price and availability.
At 2TB they diverge: the WD20EZBX is conventional while the WD20EZAZ is shingled, and Toshiba's 2TB P300 is conventional. Reading the part number matters most at this capacity.
At 4TB it inverts: WD's 4TB Blue is conventional and Toshiba's 4TB P300 is shingled.
At 6TB both makers' models at that capacity are shingled, which is worth knowing before assuming the larger drive is the safer one.
None of that follows a pattern you could guess, which is the point of resolving per part number.
Availability is the honest one. Seagate and Western Digital dominate retail shelf space in most markets, and Toshiba's consumer drives are more variable in stock and sometimes cheaper as a result.
Rotational speed differs where the mechanisms differ: the conventional Toshiba models are 7200rpm and the shingled ones 5400rpm, which follows the mechanism rather than being a deliberate tiering choice.
Neither line is a NAS drive. Both are desktop-rated with desktop warranties, and if the storage is going into an array the answer is a NAS line from either maker rather than a comparison between these two.
The case against either is the same: both are desktop lines that people buy for arrays because the price is attractive, and in both families the shingled models sit next to the conventional ones under the same product name. Buying a WD Blue because the last one was conventional, or a P300 because the 1TB was, is exactly how people end up with a shingled drive in a NAS. The recording answer belongs to the part number, not to the family, and neither family is a NAS family regardless.
It depends on the capacity and neither follows an intuitive pattern. WD is conventional at 1TB and 4TB and shingled at 2TB and 6TB in the Blue 3.5-inch line. Toshiba is conventional at 1TB to 3TB and shingled at 4TB and 6TB. Check the part number rather than the brand.
They are closely matched: the WD10EZEX and the DT01ACA100 are both conventionally recorded 7200rpm drives. Price and availability should decide it, and Western Digital generally has wider retail distribution.
Both publish it, which is the outcome of the 2020 episode when shingled drives were shipping into NAS-marketed lines without disclosure. Western Digital publishes a model-level client SMR list; Toshiba states it in product documentation and named specific SKUs in an April 2020 statement.
Neither is a NAS line. Both are desktop-rated with desktop warranties and duty cycles, and both contain shingled models. For an array, buy WD Red Plus, Toshiba N300 or Seagate IronWolf, all of which are conventionally recorded across their ranges.