UK Standard Visitor visa confusion -- 'Other' or 'Business related' for attending a training/workshop as a researcher?

I am quite confused about the "Reason" I should choose in the window below

Based on what you wrote, you can select "Other" and when the description text box opens...

• give a brief description and mention that the event's glossy (along with your registration/invitation info) is included in your evidence bundle;
• cite the exact paragraph (and subparagraph if there is one) from Appendix 3 of Appendix V of the rules that best covers what you will be doing (an important step for your case and part of best practices for all applications)

You have 500 characters which should be enough, but can continue to a separate sheet if need be (this is unwise because it invites the conclusion that your application is complex).

Will you be paid for any of your business activities while in the UK? Should I answer yes to this?

If you are travelling on a corporate expense account (as I understand it), then the answer is no, you will not be paid. The rules allow a person to recoup their expenditures and even to receive a small honorarium.

You will have to make the relevant disclosures in this question...

I have already contacted 'UK Visas and Immigration' and their simple answer was: "We cannot help you with that, you should choose the correct one for yourself"!

This is normal and no cause for alarm. Their instructions are to feed back what is published on their site and nothing more, and they are not supposed to delve into anything to the extent where the person becomes a "particular individual" as defined by the 1999 Act.