What are the best real estate companies (不動産) for new and used mansions in Tokyo?

I've begun looking into buying real estate, considering both new and used (~5 years) mansions. I understand that typically one would either use an agent (like Suumo) or directly engage with real estate companies when buying. Right now, I'm interested in 3LDK, approximately 70m². I have a few questions and could use some collective wisdom:

1. Is there a ranking of the best real estate companies based on factors like quality and maintenance?
2. Are there any companies that should be avoided?
3. What pitfalls should I be aware of?
4. Has anyone used Suumo Counter? It's supposedly a free service, but I wonder if I'll end up having to pay for it in the price difference of the property.

I've found some articles online, but they seem sponsored, as the drawbacks listed are usually minor. Therefore, I'd appreciate hearing about personal experiences.