There are some important things you need to consider:
1. Operating system
There are several OS used in hosting business but two most common are Windows and Linux.
2. Hardware
Hardware is the heart of the server if you have good hardware you get good performance.
3. Bandwidth
Dedicated servers use for heavily loaded websites so that there will be no data transfer issue.
4. Support
The quality of support matters if the provider have technical staff who have answers for your hardware and software issues.
5. Upgrade Options
You need to check with provider if they can upgrade your package in future for your upcoming needs.
6. Pricing
You need to check market where you can find best price for your needs.