Based on my listed needs, which email client fulfills the most?

I am looking for an email client, I don't know if Apple's Mail.app is the one that suits my needs best but there are so many options i felt i should defer to the community. I first am going to list my needs and then what i have read about each client so far (from searching around the web are reading reviews/forum posts/etc).

My needs are as follows:

1. 
   

   I have many email accounts, a few Gmail Accounts, a hotmail account, a Gmail Apps mail account (which is basically an outside domain which uses gmails mail as a way to access their email - i am specifically referring to my university email), as well as a couple domain name registered email accounts (custom domains i manage). I need a client which can support many accounts of different types. I prefer different accounts to have different inboxes so the client should separate each accounts inbox, trash, archives, folders, etc all separately.

   
   


2. 
   

   I receive a lot of emails that often require urgent attention, as a result i would like to have notification pop up on my mac. And it would be great if i could integrate it with my notifications center since i currently don't use that for much but would like to learn to get used to it.

   
   


3. I would like a client that has conversation view like Gmails web mailbox. Not one like Thunderbirds plug-in which simple appends to the back the related emails, because that doesn't reduce the amount of items in your inbox, it just links them.


4. I would like a client with a smooth UI that is easy and intuitive to use.


5. I would like to be able to sync (or at least import) my contacts from my Google Account


6. I would prefer a client that can integrate with my google account, as well as other apps.


7. I would prefer something that doesn't eat up a ton of RAM, i realize that the more accounts i have on it the more RAM it will use, but i would like something decently efficient

Here are some things I have heard/my experiences with other clients.

ThunderBird is the only client I have actually tried so far and i found it had a lot of bugs for me. Often times i would receive and email and no notification would pop up at all even though if i went to the app it would be there in my inbox. Moreover when i installed Conversation View plug-in it seemed to do it in a way where each time i received an email for an old conversation i would get a new inbox message and it would simply append the old conversations to it so it never actually reduced the amount of emails in the list (e.g. if i went to an older email in the same "conversation" it wouldnt have the newer emails after it, since it was its own separate file in the list of emails.

Airmail is the app i hear the most about, but there are dozens upon dozens of bad reviews for Airmail 2 on the app store page. Did Airmail 2 really just fuck everything up?

Mailbox is a no go for me, i hear it is absolutely amazing but since it only works with gmail and icloud it is useless to me for my hotmail and domain registered emails.

PostBox is a client i hear a ton of mixed signals about, I hear it is a fork of thunderbird and thus doesn't have true OSX integration which means it would probably lack a lot of the notification features (the same features that Thunderbird had huge bugs with).

Mail.app is Apple's own mail app and I actually have never even given it a chance because I just hear so many complaints about it. I don't know if those issues have been fixed but I always hear that there are better apps out there for mail clients than this one.

Inky Doesn't seem for me due to it's fundamental nature of being super simplistic. I like having the ability to do a little more complex things with my mail than just receive and reply.

Unibox seems interesting but I hear that Airmail is usually just better at doing what Unibox tries to do

MailMate simply scares me. It has a huge price tag and is supposed to offer everything but the kitchen sink. It's UI isn't that pretty and although I like to think of myself as more of a power-user than most people, i don't see myself using this tool anytime soon.

So what are your thoughts of the email client you use and why do you use it? I am really leaning towards AirMail 2 right now but the reviews scare me.