At a minimum I would like to see added:
Spitfire LF.Mk VIIIc (full span, universal wing, Merlin 66 at +18lbs boost)
Bf109G-14 (Bf109G-6 with MW50, top speed about 420mph, fills the gap between the Bf109G-6 and Bf109G-10)
Boost on the Spitfire Mk V reduced to +12lbs boost.
Here is the complete Spitfire lineup I'd really like to see:
Here is my prefered list:
1940: Spitfire Mk Ia (increase performance to +12lbs boost levels)
1941-1942: Spitfire Mk Vc, +12lbs boost (120 rounds per cannon, but reduce the boost to 1941 levels so Merlin 45 at +12lbs boost)
1942-1943: Spitfire F.Mk IXc (remove the options for the .50 cals, rockets and 250lb bombs, otherwise keep it as it is with Merlin 61 at +15lbs boost.)
1943-1944: Spitfire LF.Mk VIII (Merlin 66 at +18lbs boost, full length Universal wings. Can stand in for the 1943 LF.Mk IX as well as be suitable for Med. and Pac. theatre usage)
1944-1945: Spitfire F.Mk XIV, +21lbs boost (Keep the armament options, but raise the boost to the +21lbs level to justify it's perked status and keep it as the ultimate Spitfire in AH)
1944-1945: Spitfire LF.Mk XVIe, +25lbs boost (clipped wing and perhaps bubble canopy as the Mk VIII is available to stand in for the high back Mk IX in 1943/44. This would be the ultimate free Spitfire)
Royal Navy: Seafire L.Mk III (the most common wartime Seafire)
In total those six Spitfires and one Seafire give the most comprehensive coverage of Spitfires/Seafires that saw service in WWII while keeping the total number of units to a minimum.
See this recent thread for an extensive discussion about it:
Suggested, complete Spitfire lineup for Aces High