From an ex-109 pilot: the 190 is superior plane for air combat.
It is pretty simple. 190 is made to fight at high speeds and is well equipped for those short snapshot opportunities. While 109 is a superior plane for 1 on 1 dueling type of fights, it is never as good in many vs many as the 190 is. To make a kill, 109 has to slow down. Everything takes longer, enemy has more time for evasive actions, and most important - slowing down in a crowded arena like AH is a big no-no. Flying the 109 in early AH beta was easier, slow down today and someone will nail you. When in 190, you have the luxury of making kills while staying fast, great snapshot lethality, much better visibility, greater range, durability and dive. Even when missing half wing you can make a kill if staying fast
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The 190 is not a dueler's plane. Of course you have some tricks to resort to when pressed into a duel, but you generally don't want to be drawn into such types of engagements. Instead, work for your advantage before the fight. First in term of alt advantage, then speed. Just be sure to have enough speed when entering a fight. Always watch the speed indicator - never let it go below 300 IAS. You will be much safer that way and yes - much more lethal. Your enemies will have less time to react.
When in fight, don't go for E conserving moves if they slow you down. Use nose down maneuvers instead, you wan't to stay fast and come up at your enemy guns blazing. Use the 4 20mm, flying around with only 2 20mm is a waste.
Practice gunnery and snapshots. As much as 90% of your kills will come from snapshots. While you pack a great punch, do not HO. 9 out of 10 planes in AH will take the HO. You will kill them, but they will probably damage you or even kill you.
At high speeds you can even turn inside several plane types. If you chase a Spit at 400 IAS and he goes into a turn, you can turn inside it and pull enough lead to kill it. Just be sure that other enemies are not around, better stay fast then. Fast roll rate helps you match enemy moves at high speeds - you can spot when they roll into a turn or Split S, roll to follow and pull quickly and ping them. This is one of the greatest things when flying the 190. 190A is much better at high speed instantenous (sp) maneuvering than the D-9, which is simply a different plane.
Speed is your defense. Never allow yourself to fight from disadvantage, why would you give your enemy an easy kill. When he gets the advantage, you better be on the way to pack of friendlies or even better - your ack. But in the desperate situations you will be forced to defend yourself. High speed again. Keep rolling, preferably out of sight of the enemy. You can change your lift vector orientation quite fast in that plane. Roll under enemy's nose, use any scissors you can think of, just stay fast. Against most fast planes you can create an overshoot easy. Practice flying while looking back. match enemy moves. Be ready for a brief snapshot and then go back to being fast again. Maybe a time to extend too.
Use split S while in 109 it is not a smart move generally, it has sense when flying 190. Quite a few get surprised by it, especially when you get out of it guns blazing.
If high enemies are around be sure to pull into them when they dive on you. try to create separation or take a HO if there is no other way. Be careful about turning your back to the enemy.
Even though defense in 190A can be fun against some planes (P51 mostly), it is fighting a losing fight. Remember that.
find a wingman, or better, a squad. No plane benefits out of group flying as the 190. While fairly hopeless in 1 on 1, it rules in many vs many type of fights.
And last thing:
Vulch, vulch, vulch !
