Realistically, these characters are the same. At the end of the day you will end up playing them the same. That's DOA4 for you.
However, you can't be aggressive with Ein, Jann Lee can get away with aggressive play, somewhat.
Ein, you will have to space a lot, and do a lot of poking. The lot of his moves are unsafe, and not just a little unsafe. he has a few safe moves but most of those are slow, like
20i~28i+ . You could do those moves to throw people off randomly but, I don't adivse to keep putting them on the screen.
The moves are:
2 
(28i) it guard breaks,
45 (20i) it guard breaks. (This move does not have the range that Hayate has with it),
236 (33i),
(28i),
3 (30i). These are just several moves, he may have a couple more.
One of his useful safe moves is
3 , to benefit you don't spam the move, use it when it's needed. The start of it is a mid kick and Ein's good moves are mostly in the mid area. So you need to be caution of that especially playing against characters with great mid kick holds.
Ein does have a true mid,
6 , and the stun it gives is very problematic. If your opponent is hit with it, they have to make an immediate decision, to hold or not to hold. Of coursse holding out of it grants you that very powerful
12i throw Ein has
33 , if your opponent holds high or mid. The low throw is not as great as that one, but it gets the job done. Still, in this situation, it is always going to be a 50/50 situation, so your reading skills and applying a strong yomi game is what you will need to get what you want from the stun. Also, this move is very unsafe if blocked or whiffed, do not overly use it.
You could also extend the stun, for opponents that won't hold, but you could be held at any time while doing that. So, watch yourself.
Playing with Ein you can't be "aggressive", you must take your time when playing him. He has the tools to space with (
3 ,
6 ,
4 , to name some) to keep players out and once he gets in he can do his fair share of damage. Those moves are unsafe, with the exception of
3 it has follow ups that should be respected.
For his
6 , do it when players rush carelessly, nothing they do will beat it. It can't be crushed, they could jab you to stop it but the hitbox of this punch compared to a jab is massive. So with the jab being out of range, it too will get stuffed.
Watch characters with an OH that can done with
, you could hit them in the start of their OH, but if your timing is off, you will get OH doing that punch.
4 is good for its range, against non-teching players you could start a ground game (
1) from this kick hitting them. The hitbox of the move is fairly decent, use this kick for players that like to attack to cover ground. The kick will hit them while they are doing this, of course you need to be in the area of them doing this. This kick also launches on counter hit.
3 is also good for its range, its a critcal hit and stun and, on counter hit it puts your opponent in a sit-down stun. Another situation (50/50) where their option is to hold or not to hold. It's on your yomi game how things will go.
Now, just because I suggested when to do these moves does not make it the only time to do them. I just know in the said situations I gave, those moves rape with ease. I am pretty sure you can find other situations where those moves will work just as well if not better.
Ein's launchers are:
9 ,
9 ,
4 ,
8 (this move has a slow start up and can be seen easily), and his
while rising from the crouch position. Ein's
3 has luanching capabilities, I am sure he has a few more launching moves. With these, mix them up when you decide to use them.
Basic Juggles:
6 and
16. those are the only ones that I know of. The second juggle covers ground and can lead up to some wall damage. Also,
62 for floor damage, floors that explode.
I can give some more stuff on Jann Lee, later, if someone else doesn't get to it before me.
