Is it better to use tabs instead of a dropdown menu in a contact form?
Actually there are 3 options(maybe even more?). And they all have their benefits and detriments.
When would we want which?
The most obvious choice you have to make is how much space you can assign. If you can, or even need, to fill a lot of space, you can go with a two-pane design. If you don't want to use a lot of space, you'll have to shrink either the contact-option list, or the form.
Question 1: Can you afford to take up a lot of space?
The second choice here is based on a few factors, butbasic trade-off is this: time spent in the contact form, versus time spent reaching the right person after the contact form.
The dropdown allows me to pick a department, but many users will not make those 2 clicks and just contact the default/first of the list. This will lead to higher amounts of traffic to that department. It can also cost the end-user more time; I contact the default (support desk) which then has to redirect me to my goal (sales dept).
Alternatively, the accordion forces me to choose, which will spread the contact load across all the departments a bit more evenly. It'll also reduce the amount of 'I will put you through to X dept' emails. But it'll have a slightly higher amount of people incorrectly contacting the wrong department;
"Hello is this sales? Yes your sales software is offline so I can't sell cars right now."
"I'm sorry but that is a technical problem, I will put you through."
Question 2: Do you (want to) have a general contact department that filters contact requests and takes off some load off the specific departments?
Forget the tabs.
If you have just 5 options use a radio button instead of a dropdown: users will see all options in the first place and they won't need to display the list to start thinking who they should contact to.
If you have a really long list of options both radio buttons and a dropdown will be bad ideas. I would go for another approach, like giving fewer options and instruct recipients (inside the organisation) to forward emails based on the contact form contents.
Additionally, I would change the label "Contact the sector you need" for something the user knows, like "Your contact inquiry is regarding to". The first label assumes the user knows your organisation chart while the second relies on user previous knowledge.
Both of the options can provide good user experience if they are used properly.
In your case, the drop-down provides a better user experience for the following reasons:
Tabs are good when you have content that is different in each section. Drop downs are good for selecting a variable in one field.
The tabs feel separate from the contact us form itself and almost create 5 different contact us forms. I feel like the user could miss that step entirely and you will get more submissions to Sector 1 because that is the default tab.
The dropdown fits better in to the steps of the contact us form, and provides users with an easy to read, step-by-step approach. You could even remove Sector 1 as the default selection of the dropdown, and make it required. That way the user is more likely to select the correct Sector because they will be prompted to go back and select a sector in the case that they missed the dropdown.
Both of them work from a user's perspective, but, I think you will be more likely to get the submission to the correct sector with the dropdown approach.
Tab is for navigation, drop-down is for input.
Though tab can be used for input like you have done, I feel it is not a good thing to do. I was confused by the first design, as to, what should be done here. Do I Need to fill the form on each and every tab?
I would go with the drop-down.