I chose Midway, because I am a naval enthusiast. Battles are important for different reasons, turning points, halting an advance, breaking an enemies forces down, and so forth. Of the listed battles, Midway was a very important turning point in the Pacific and probably the single most important naval battle of WWII.

One battle that is never discussed is the battle of the Atlantic, now what would have happened if that one was lost.

Afaics,IMHO,from my POV,and such things,the Germans were never nearing the point that they could win the Battle of the Atlantic .
Some figures about the U boats:
1 january 1942:249
58 in the Baltic for basic training
100 for advanced training
of the 91 remaining,only 55 were available in the Atlantic ,of which 22 operational .
In 1941,the submarines sank 2.1 million ton of shipping
In march 1943,there were 400 UBoats
52 for basic training
119 for advanced traning
7 experimental boats
222 front-line boats
182 stationed in the atlantic and 40 elsewhere
Of those in the Atlantic
68 at base
44 en route
70 on combat patrol,of which 45 patrolling the convoy routes in the North Atlantic

from Naval History the losses of the British,allied and neutral merchant navies in the Atlantic ocean ,from all causes.
1939:O.3 million ton 35 boats 5 UBoats were lost
1940:1.739 million ton 330 boats 12 Uboats were lost
1941:2.557 million ton 525 boats 23 UBoats were lost
1942:5.834 million ton 1188 boats 69 UBoats were lost
1943:1.92 million ton 328 boats 164 UBoats were lost
1944: O.225 million ton 40 boats 111 UBoats were lost
1945: 0.132 million ton 21 boats 16 UBoats were lost

Originally Posted by LeEnfield

One battle that is never discussed is the battle of the Atlantic, now what would have happened if that one was lost.

This one I remember ; it was fought desperately and personally by those like my uncles Fred and George, one who just missed the sinking of his ship HMS Hood through urgent call to subs and then was sunk twice more before the end of the war. The other a merchant marine stoker racing the Atlantic throughout WW11. Both survived to tell the tale, which led to my going to sea as soon as I left school - Ist opportunity.

I recall the defences around the North Sea coast of Scotland, I played in them daily, crawling through the continuous trenches, climbing the concrete block vehicle stoppers, inhabiting the pill boxes. We lived under threat constantly.

We could not have lost this one.

Originally Posted by LeEnfield

One battle that is never discussed is the battle of the Atlantic, now what would have happened if that one was lost.

While it was very important, the "Battle of the Atlantic" was more like a campaign in my way of thinking, a series of many separate battles fought over a period of years in a large theater of operations.

Thousands of men died and thousands of ships lost, still unless it is fought on land then it doesn't count, or so it appears.

Originally Posted by LeEnfield

Thousands of men died and thousands of ships lost, still unless it is fought on land then it doesn't count, or so it appears.

It matters to me, I picked The Battle of Midway, all I was saying is that the Battle of the Atlantic was bigger than one battle, more like a campaign, it was a very important campaign consisting of many smaller battles. In my way of thinking a battle is a discrete action, taking place in a specific location and over a period of hours, days, or even many weeks - Like Stalingrad. An ocean is a very broad site for a single battle, and years is longer than a single battle in my way of thinking. This is only my opinion, and I in no way intend to demean the importance of this critical campaign for the survival of Britain. Comparing the Battle of the Atlantic to the other battles on the list, made me think of a campaign - which could be called a battle (like the Battle for France, the Battle for Germany) - but has a more descriptive term (campaign) available.

I agree it is not that the Atlantic campaign was not important that it is not listed here but rather that it was a theatre of operations comprising many individual battles and as such is not really a "decisive battle".

Midway was the most decisive battle in my opinion, it ended any hopes the Japanese had of ever winning