Well, if you can MASTER 109s, you are a truly great pilot. Same goes for any plane. LEARNING to fly it is relatively easy. Mastering it? Not so much.
Here's the thing: 30mm ballistics suck. 109K-4 flight envelope rocks, though. It's got gobs of power, super climb, great WEP, and decent range. I've had my personal best at 8 kills without reloading in one.
On the other hand, several times I've gotten 8-10 kills in a P-38 as well. Even after you run out of 20mm the gun package (situated as it is) is still superbly lethal! It's got range, it's got redundancy (letting you limp home on 1 engine), but it's also got poor views all around.
The landing gear isn't really the problem. It's the torque. Single engine planes (and most twins) roll/pull to one direction because of the spinning prop, and the K-4 has this in spades. So landing a K4 is going to be a LOT more difficult than a P-38, because in the p38 you only have to worry about 2 axes, not 3.
So the 38 is fairly easy to fly, but limited in the moves it can do compared to some planes. Vertical ropes, loops, hammerheads, etc are the most effective when it has some speed, as it is a great looper. Flat turns are mostly bad. It doesn't do prolonged nose-high turns at all. Nose-low spirals work well. Roll isn't great (it's a huge plane, takes a while to haul around). 109K turns well, can spiral climb nose-high (mostly because of the engine) but it has to worry about torque. Very few things can run away from a K-4 in this game. Only the top 10 climbers can outclimb it.
2 very different but very ballanced choices. Personally I'd go for both!
It helps to learn more than 1 plane. You lock yourself in and you'll miss out on things that you can't do in "Brand X" plane.