It perhaps sounds a bit more positive than it is.
For FS9 there is a huge collection of Bf109s. From the early Jumo 210 engined versions, all the way up alanog all the Daimler Benz engined versions, to end with an experimental version with the Jumo 213 engine.
I have never tried, so I can't say all these models will work in FSX.
When you look at the choice you have in native FSX Bf109 models, the choice is limited.
A2A has a free update for their FS2004 Bf109E model, which turns the model into a native FSX model. This update more or less replaces everything except the textures. Really nice model, which contains some errors, but so minor I can live with them. The package contains several sub-version for all theatres of war where it was active. There is a huge amount of free repaints available for this model. Mainly based on the stunning paintkit by Martin "ICDP" Catney.
JustFlight has a native BF109E model, which was done by the people from Aeroplane Heaven. Like all models it has strong and weak points. Personally I don't really like the textures, but the model is definitely good.
Flight Replicas has a nice Bf109 K4 (Kurfurst) package which is more or less the last production version of the Bf109. Great model, although I personally would like some more clickable items.
Flight Replicas also has a Bf109 G6 (Gustav) package which is the main production version of the Bf109. Like the K4 version a great model, which could do with some more clickable items.
From the same designer is the Messerschmitt Bf-109Z "Zwilling" which is the tandem version of the Bf109. I don't have this model (yet) so I can't comment. But like with all FR models the looks are definitely great.
Flight Replicas also has a Hispano Aviación HA-1112-M1L Buchón package. This is the Spanish produced version of the Bf109 G2 equipped with an Rolls Royce Merlin engine. Another great model.
Preference is something personal. When I could only have one, I would purchase the Bf109E by A2A. With only $9.99 and a free update into FSX native an absolute bargain. Second would be the Bf109 G6 package by Flight Replicas. The model is really a piece of art. The Buchon would be my third choice, as it is something special.
Cheers,
Huub