I use Biblioplan now at grammar level and am very happy with it. But I will seriously look at TOG for logic stage. I don't have an answer for you one way or the other, but a few things I would look at:
-Biblioplan is just history. Are you likely to use TOG for literature, art, etc. (I'm not sure what all it includes), or are you mainly using it for history? If you want the other stuff, it would make sense to go with TOG.
-Cost difference. Biblioplan is ~$25 for a year, and I think TOG is ~$225. How much are TQ guides and how many are needed for one year? Do you already have them? Are you on a tight budget? Could $200 help significantly with other home school needs?
-Difference in style between TQ discussion questions and TOG teacher helps? I haven't seen either, but this could be a big factor for me. If one set was closer to my philosophy/teaching style, that could swing it for me. Have you been able to see both?
I have not really looked at TOG, but from various posts I get the feeling that there is a lot of overlap in books used by it and Biblioplan. Sorry I can't offer more help--let us know what you decide! We'll be there in a couple of years!