That's great to hear you used SCI Companion for your contest entry! (me too, of course)
As for interpreters, my favorite way is to run sciv.exe in DOSBOX Although DOSBOX is noticeably slower than running sciv.exe natively on XP, I like the fact that it's in a window, and it seems to crash less often than XP's dos virtual machine.
I've tried FreeSCI, but it had some different behaviour than sierra's sciv.exe interpreter - notably it treated some Said strings differently (which was making my game unplayable), and also I tried using the file operation kernel functions, and they behaved completely differently in FreeSCI. I opened bugs against freesci for these about a year ago - I don't know if they've been fixed on a later build since I haven't checked it out lately.