Which is better: Spendor BC1, SP1/2, or SP2/3.

My experience is with the smaller, more WAF Spendors, wherein I'll recommend that you chase the Classic S3/1p, which is like the 3/5 except that with a vented 6.5", and therefore has much greater extension, while also being +4dB more efficient. I use a pair of these along with the excellent SC3 (like the 3/5 but with a second mid-woofer) to make a seamless HT front trio. Forgiving up top, extremely natural mids. I use a sub in this system, so the larger Spendors would be inappropriate.
The Boston Spendor dealer still loves the SP1/3, and sells them to us old farts who can accept the archaic box geometry!

If you can get mint BC1s, they had a magical sound that was somewhat lost with the following iterations, SP1s and the rest. They also had a slightly underdamped bass that modern amplifiers would have no problem with. Lots of warm bass and clarity but volume limited.

Personnaly, i've just bought a pair of BC1, at first, i tought too much base and unprecise, than i've built a speaker stand with rosewood/pine/rosewood with pike.

Then magical appear, it was/is like the band is in my place, never heard a warm speaker like that before, except in the 80's when i was a student. I've own a pair of Tannoy mercury than a Tannoy Jupiter. There's something spécial in those speaker that took me over 20 years to find back! But what a result!

BC1 defetely an absolute, espacialy if you enjoy small band music(Jazz or Folk).

Has anyone compared the BC1 with the B&W DM2 from the same era?

Both have the same top end with Goodmans tweeter and Coles super-tweeter but the bass/mids driver differs as well as the cabinet which in the DM2 is an acoustic line design whereas in the BC1 is ported.

The SP1/2 and the SP1/2R2 are different animals. R2 is brighter.