Most Marine Chapters are based upon a martial archetype. This is, in and of itself not necessarily a bad thing, in my view. I don't think there's anything inherently wrong with the Space Wolves being Vikings in Space, or the Ultramarines being Romans in Space. It annoys some people, but it';s not a problem for me.
To go back to the OP's point, in common with a few others here, I also dislike the Dark Angels. Specifically, I dislike their angst-ridden, overblown 10,000 year guilt trip, and their inconsistent development. They don't hang together well for me as a Chapter. At times in their history they've been Native Americans in Space and at others Space Templars. The martial archetypes applied to them are all over the place, their secrecy and intrigues are pointless and endless. So much of the writing that surrounds them come across as wangst rather than true, powerful drama. To a degree this criticism arises as a result of the multiple authors who have worked on them over the years, but other chapters have come off far better from this same process. When I've raised these points before, others have argued that the inconsistencies are inevitable for a chapter with a 10,000 years history, which is a fair point. But I still don't like them. The Dark Templars do "Space Knights" much better, and the Relictors do "Marines with a hidden agenda" better.
Their miniatures are really nice, though.
As for my favourite chapter, I have a few homebrew chapters bubbling away that I'm fond of, if only because I've been painting their armies for the past 15 years. (I paint veeeery slowly.) Canon chapters I like include the Fire Hawks (because they're such arrogant scumbags), the Lamenters and the Star Phantoms. In fact, the excellent write ups contained for all chapters involved in the Badab War, as set out in the books by Alan Bligh sold me on a lot of the Chapters involved in that conflict, an excellent example of how a good write-up can make a chapter come alive for even a jaded old fan like me.
If I had to pick a Legion/Chapter I've always really liked, it would have to be the Death Guard. Ever since I first saw their write-up in Lost and the Damned, I've loved them. (I spent ages painting up a loyalist successor chapter which bore DG geneseed before I realised what a terrible old cliche that was!) I like their pre-heresy colour scheme, their toughness, their love of brutal attritional warfare. I'm very excited about the new Forgeworld book which will cover them (and three other legions) in detail.