Most of them are pretty rubbish... What are you actually wanting to deter against? The cheaper ones (Oxford in particular) can still mostly be cut with compact bolt cutters, the bigger ones usually fairly large ones, then the best like Almax and the big Pragmasis are cropper proof, takes hydraulics or noisy attacks to break them. But on the downside are expensive and HUGE.
The cheap Oxfords are a fairly reasonable low-security lock as long as it's cheap, they're not too heavy and will protect you from the lowest level knobbers unlike cable locks etc. But anyone who wants the bike will still walk away with it in about 20 seconds.
D-lock is best if that'll fit round your street furniture of choice.