Last summer, I went back and forth between SL and TOG. My daughter was starting first grade, and my son was starting k4. I wanted to pick a program that I felt comfortable sticking with for the long haul. I agree that both have their benefits, but I ended up choosing TOG for the following reasons:
1. It is much better suited to multi-age teaching. I really wanted something that allowed me to keep my kids studying the same core material. My 4 year old and 6 year old have both studied the ancients and really enjoyed the whole year. It is nice to know that when my littlest one (now 1) is ready for school, she will be studying the same material as her big siblings, but at an age-appropriate level.
2. I like TOG's approach to history (traditional classical, with 3 rotations through all of world history). SL seemed less organized in its approach.
3. With TOG, you can reuse so much of the material. You only have to buy 1 set of each year plan, so after the first four years, you have all the core curriculum you need for the rest of your children's schooling and just need to add the books (and math & science).
I have really liked TOG, and I'm very glad I picked it. The lesson planning has not been too onerous for us, and I like having so much say over the kids' lessons. I feel like I probably would have "tweaked" sonlight so much that lesson planning would have taken twice as much time as it did with TOG.