Same fabric, same weight, same print. The difference is a hood and a collar, and it changes more about the garment than people expect.
Where the hoodie wins
Weather. The hood is genuinely useful in drizzle, which in this country is most of the time. It is also the reason a hoodie works as an outer layer on mild days when a sweatshirt would need a coat over it.
Adjustability. Hood up, hood down, drawstrings tight or loose. A sweatshirt has one setting.
Where the sweatshirt wins
Under a coat. A hood bunches at the back of the neck under any jacket with a collar. If your winter routine involves a proper coat, a crew neck sits flat and is more comfortable all day.
Smart-casual. A crew neck under a jacket reads as deliberate. A hoodie under a jacket reads as a hoodie under a jacket. Depending on where you work, that matters.
Print visibility. Without a hood and drawstrings, the chest area is cleaner. Larger designs sit better on a crew neck.
Warmth
At equal fabric weight the hoodie is warmer, and almost all of that comes from the hood covering your head and neck. Down, the difference is small.
Which to buy first
If you own neither: hoodie. It covers more situations, and in a climate like ours the hood earns its place. If you already own three hoodies and reach for a coat every morning anyway, the sweatshirt is the more useful addition.
Our range
Many designs are available in both — the hoodie range and the wider unisex clothing section overlap considerably. Check the fabric weight in the Materials section on each product page, since that varies more than the style does.
Related: how to choose a hoodie that lasts and layering for British autumn.
Further reading: Wikipedia: Sweatshirt