A first choice for me would be the Lloyd as it's not available in plastic and especially if a 6pdr came along too!! Plus there are 4 distinct versions that come form it that are significently different but based on the basic vehicle. Much more interesting.
The Versions were
Carrier Personnel
Carrier Tracked Towing (for the 6pdr)
carrier Tracked Towing (4.2 inch Mortar) requires a trailer
Carrier Tracked Starting and Charging
If a new carrier was coming along then I'd go for a Mk I as again as 2 x Mk IIs already exists and the Mk I soldiered on throughout the war in all theaters of operations, so you have a vehicle that can be used in any WW2 time frame.
The current Tamiya Mk II kit even given it's age and it's faults can be fixed up as the main weakness is the tracks, drive wheel and the thickness of the frontal armour. All the basic Mk II versions are the same with diifferent stowage/radios for HQ Carrier, PL carrier, Section Commanders Carrier, and basic Section vehicle.
Mortat Carriers
There weer 4 versions based on the Mk I chassis the only main difference being the engine. One version was Canadian Built.
There were 4 versions based on the Mk II carrier, again different engines and again one based on a Canadian vehicle.
Medium Machine Gun Carrier
There were 4 versions based on the Mk I Carrier.
There were 4 versions based on the Mk II Carrier
There were 3 versions somewhat unique to Australia.
AOP Carrier
1 version based on the Mk 1 and 1 Based on the Mk II, with 4 based on the Mk III
So either the Mk I or Mk II would easily produce the AOP, 3 inch Mortar Carrier and MG Carrier and all could be further divided into PL, Sec Comd, and Basic vehicle, but the Mk I has a wider time frame.
I'd still prefer a Loyd
Al
Edit:
WASP Mk I and Mk II
All designed on the Mk I Chassis.
Originally
Ronson - Canadian design based on the Mk I
WASP Mk I - British design mounted on the Mk I
WASP Mk II - Britrish design mounted on the Mk i
Wasp Mk IIc - British design mounted on the Mk I then modified by the Canadians and tested on the T 16.
Sorry the Mk I has it in my eyes despite what's been said about the Mk II as it fits the bill for every version.
Al