i have a chanel m/l black caviar flap. i've used it once. i love it and i know that it's classic and i can wear it in many different ways for many different occasions. i actually have a chanel diamond shine i wear more because it's bigger and more casual (though it can be dressy) and it just suits my lifestyle better. that being said though i know my caviar flap is something i will have forever and will use time and time again. i think the balenciaga, speedy, etc are nice bags too. but they are more casual bags. i think you need to think about what you want it for. if it's weekends, nights out, weddings etc then i think the m/l flap is a great choice. you will never regret having it and yes, i think it is a great bag to pass down. if you want something you can use more than perhaps the other bags plus shoes are a better choice.
have you thought about buying a pre-owned or even new m/l flap on ebay? you could probably get a deal on one and then still have money left over for something else. they come up pretty frequently i think.
the only thing i regret about my m/l flap is that it is gold hardware. i think i would like it better with silver. but my diamond shine has dark silver and my other chanel flap (purple caviar e/w) has silver so this is something different.
ooh, that made me think- have you thought about an e/w? it's really to small for anything but evening imo but it's cheaper and still a great bag!
