It seems unlikely that the UK would be happy to go along with a US Operation Sledgehammer by unblooded US forces. It seems less likely the US would do it alone. The Canadians will still want to "do something" before their neighbours arrive, so Dieppe / Jubilee will likely happen. Hopefully, Valentine's Tanks (briefly getting back to the POD here) can climb shale beaches better than a Churchill. When Jubilee fails, the British & Empire forces will be even less keen on Sledgehammer.
That leaves Norway or the Med. Fortitude North would take a lot of pressure off the convoys to Stalin (Kûrvi-Tasch; I believe a fellow Tintin-phile called him), and provide the WAllies with quality Iron Ore from Narvik. However, it involves attacking a large German army in inhospitable terrain and rough weather. The only place it leads to is Finland, and although there is a remote chance to liberate Estonia after Zitadelle fails and the Red Army is able to overpower the Germans, it's not the continent.
The Med will be an Island-Hopping campaign, which is the same as the US Navy & Marines may be prepared for. (Ironically, this war may see Island Hopping in the ETO and field armies in the Pacific). The East Med is more convenient for the Empire, as it is closer to key nodes & the 8th Army. Hence the plan to "practice" in Rhodes.
With Sicily splitting the Med, and the long way around being very inefficient for shipping, it seems unlikely the Americans will want to attack in the East Med. It is also quite out of the way and running around in the Balkans is more Churchillian than American. That leaves Vichy North Africa or Corsica, Sardegnia & Sicily. FNA is a source of Iron Ore but against a weaker opponent than the Wehrmacht. Arguably it's a fringe operation, but it does secure the Allied flanks. Corsica and Sicily are much closer to enemy air power. Sardinia is not so much.
As noted, Sardegna has a major port, is Italian, and is well located to function as an "unsinkable aircraft carrier". It projects power towards the other two islands and threatens the Axis from Perpignan to Palermo. It is impossible for the enemy to reinforce and so is a guaranteed American win as soon as the US Navy arrives.
Looking at a map, I would even go so far as to say that without Tunisia in Allied hands, Malta is likely insufficient to properly be a springboard to take Sicily, unless Sardinia is Allied-controlled.
But we shall see what our excellent author decides.