The only unique thing I see with GoSMS is contact signatures. However it's not enough to make me keep it. Handcent can be a little hard to find a couple of settings but at least it has all the features that make it usable.
For all I know Handcent has contact sigs too. I'll have to find 'em.
Headed back to Handcent. Not sure why everyone is doting over GoSMS?