For some reason, SharePoint Designer WF do not like sending emails to user and permission groups. One way to get around this is to create your email groups for your workflows in a separate list, then create a workflow variable to set the user names into the variable as a string. Then use the string as a collection of your user group names and set them as email addresses semicolon delimited.
Step 1. Create a separate custom list for your email group distribution. Use the ID field, the title field, and a person or group column - allow multiple users. Create your group and put all of your users for that group in your person field.
step 2. Create a variable in your workflow
Step 3. create a flag to see if it has been submitted. You would do this on the list your workflow is running from. A yes/no field will work just fine.
Step 4. If submitted = no - set workflow variable to the user group list item titled IT Senior Managers by ID on your distribution list. Set as string then, send the email using the variable in the TO: field, and set it as email address semicolon delimited. Set submitted column to yes.
step 5. you can repeat this process based off of the dropdown condition - set the workflow variable to the list item which contains your email distro list. Then, put the variable in for the TO: field on the email and set it as email semicolon delimited.
Sometimes it is best to build outside of the workflow and use what you made on the side to help run it. I use a great deal of JQuery alongside my workflows, as well as jumper/informational list like what I am telling you to build. SPD workflows suck, as a developer, you have to make them not suck. Sometimes you have to cheat a little too. Let me know if you have any questions. I hope I answered your question right.