You choose the plain 1099-R.
If there are any special treatments for it...for state tax return situations...that will be handled, either in follow-up questions after you fill in all the boxes on the main form, or sometimes in the state Q&A section when you eventually get to working on your state (if you live in a state with an income tax)
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Ther may be a question on one of the pages following that 1099-R entry...that asks if it was from a Qualified or nonqualified plan.
If you read the text where it asks...Military retirements are nonqualified plans,.
Now...if you also have a TSP account and start taking from that...that will be a separate 1099-R, and that is the same as a 401k and is "qualified"
Great, what is the 'plain' 1099-R? They are named by TT as "Financial Institution or other provider", "Office of Personnel Management", "Office of Personnel Management", and "U.S. Railroad Retirement Board". When you say "plain", do you actually mean "The one marked most common, Financial Institution or other provider"? It's amazing that TT doesn't make this more clear given the sheer number of folks who are retired military in this country.