I'd really consider adding a third server for this. Sql Server does much better when you can give it dedicated hardware. And when you add that server you're right on the cusp of where you might also want to consider putting things inside virtual machines for redundancy and simplified management. It's amazingly cool the first time you avoid a prolonged outage after a hardware failure because you just spin up a copy of your vhd on one of the other machines until the part arrives.
If you can't do this, you'll want to look at load and place your database on the server with the lowest load. Especially consider disk io here. Depending on how you use terminal server, my preference would be that the sbs server is likely your better choice, but you'll need to measure to know for sure.
And thinking about it, my favorite two-server option involves removing terminal services and giving that box primarily to sql server. Then install hyper-V or vmware on both boxes and have a terminal services instance running in each, to split the load to which ever server can handle it. You can set some users to connect to one terminal server and send the rest of your users to the other server.