This could be interesting to speculate on this since there were 19 different variations of tanks used by the British in North Africa. Many of these models were already obsolete by the time Alexander and Montgomery arrived on the scene in August of 1942.
If we follow this logic, the tanks used by the Eight Army during Montgomery's watch were the American made Grants, Stuarts, and Shermans and the British made Crusaders, Valentines, and a small number of Churchills. By the time El Alamein was fought, the Matildas in use were converted to minesweepers as Matilda Scorpions.
Andy was originally going to include a Stuart with this release but decided against it a few months ago. I doubt if the "summer surprise" will be a Sherman since the limited run of British Sherman was so recent. Could do a repaint of the Churchill but I doubt it.
That leaves the Grant, the Crusader, and the Valentine or possibly a Matilda Scorpion. Not sure how the Matilda Scorpion would do since we already had a Matilda as part of the Eight Army lineup.
In my opinion the Grant, the Crusader, and the Valentine would all do well as each is unique in its own way.
The Valentine would be my personal favorite and I think the model that could get the most mileage out of as future prospects. You could do repaint as the Russians had a number of Valentines on the Eastern Front.
The Valentine chassis could be also used to make the Bishop. The Bishop, the British first attempt at self-propelled artillery, was a boxy structure that housed a 25 pounder set on top of a Valentine tank chassis. I'd give my eye teeth to have a Bishop as part of my 1/30 collection.
Semper Fi!
Rick