It looks like things are changing...
I can understand the claim that the Hubba Hubba HAD more volume, and people have complained for years about CS 'rainbow' doors ("open door on the floor").
But the newest Copper Spur is the HV (high volume) model. It drops the 'double Y' pole configuration Hubbu Hubba and older Copper Spurs have for something closer to the classical 'X' cross poles. Just looking at it the CS HV now has more volume than Hubba Hubba. And it looks like the rainbow doors have been replaced.
So right now, both the Hubbu Hubbu and the Copper Spur look like good tents. But if I had to pick between the two of them, I'd still pick the Copper Spur simply because of weight.
CS HV = 2#12oz @ $450
Hubba = 3#7oz @$400
CS Platinum = 2#5oz... but that comes at a $150 premium of $600.
But backing up some and just speaking about tents in general...
There was a time when some 2P tents were larger than others.
The tent I use as a 2P tent is a Big Agnes Lynx Pass 2 I purchased about 5 years ago. Listed dimensions are 58x90.
I also liked the Kelty Gunnison 2.1 that was available at the time, with listed dimensions of 58x92.
But today, ALL the name-brand tent manufacturers seem to be racing for the small size to try to quote the lightest weight possible.
I just looked at all the Big Agnes 2P tents available at REI:
52"/42"x88" - typical dimensions for many BA 2P tents.
52"/42"x84" - smallest BA 2P tent available.
59"/49"x88" - largest BA 2P tent available.
And other manufacturers are matching these sizes:
55"/45"x88" - Kelty Salida
51"x89" - Kelty Gunnison
52"x88" - REI Half Dome
56"x96" - REI Half Dome Plus (perhaps the largest 2P name-brand tent I can find).
But if I were in the market for a new 2P tent, the thing I think I would be looking closely at would be what TarpTent.com has to offer.
Because they don't have traditional tent poles, they seem to provide dimensions of the actual floor space.
So as a comparison, I believe the Double Rainbow is a popular TarpTent.
Floor dimensions are quoted as 50"x88". To make a fair comparison, the AVAILABLE inside space of a Copper Spur is about 47"/37"x83" (or an average of 42"x83").
The weight is listed as 2#9oz @ $300.
The TarpTent isn't your traditional tent. It's something of a cross between a tent and a tarp. I don't think any of the models setup totally free standing. I believe all models require either trekking poles, getting staked out, or both (depending upon the model).