Must have titles

I am starting to read mysteries and I was given the complete Bantam faux leather set of Agatha Christie mystery novels. I do not have the shelf space for the whole set so I am soliciting opinions on the top ten or fifteen must-have titles to keep. I am new to the genre so any suggestions would be much appreciated.

Different people like different titles... The fact that something is popular does not mean that it will work for you...
If you want popularity - look at her page here in LT and see which books have the most copies. I guess this will be as good way as any.

I can name three must-haves: And Then There Were None, Murder on the Orient Express, and The Murder of Roger Ackroyd. They're among her best, and it would be a shame not to keep them.

I'd agree with the titles mentioned in #3; two others that would make my list very easily would be Death on the Nile and The Body in the Library

Five Little Pigs is a personal favorite, along with all of #3's suggestions.

My personal favourites are, Cards on the Table, Sleeping Murder and The Thirteen Problems (aka.The Tuesday Club Murders). There are others that are almost as good but these three are my picks.

I'd say Cards On The Table, Crooked House, Five Little Pigs, Mrs McGinty's Dead

The OP actually asked for a list of suggestions as to which were the ten or fifteen must-have titles to keep from his complete set of (80?) Bantam faux leather titles. Almost everyone who has responded so far here completely shirked this question and used his request simply as an excuse to post a list of their own few personal favorites. The OP probably moved on long ago, but since I only just found this thread, let me see if I cannot still address his original concern and provide a better answer to it. If nothing else my answer might serve as a stimulus to some further interesting discussion.

The best answer above by far was the first suggestion in post #2 to look at AC's LT author page and see which 10 to 15 AC titles are the most cataloged by the LT community. However, as that poster also caveats, this will only indicate "popularity of title ownership" and NOT which titles are AC's "most essential reads" (which is how I interpret the OP's "must-have" criterion). If you do as that poster suggested (which I just did) then you end up with the following 15 AC titles as being the most commonly cataloged by LT members:

1, And Then There Were None - 7,800 copies
2. Murder on the Orient Express - 5,700 copies
3. The Murder of Roger Ackroyd - 3,834 copies
4. Death on the Nile - 3,410 copies
5. The Mysterious Affair at Styles - 3,068 copies

6. The A.B.C. Murders - 2,769 copies
7. The Murder at the Vicarage - 2,465 copies
8. The Body in the Library - 2,367 copies
9. Evil Under the Sun - 2,009 copies
10. Curtain - 1,994 copies

11. A Murder is Announced - 1,981 copies
12. Cat Among the Pigeons - 1,965 copies
13. Cards on the Table - 1,952 copies
14. Sleeping Murder - 1,909 copies
15. 4.50 from Paddington - 1,827 copies

Just because a lot of people own a particular title doesn't mean they all actually like it. A better gauge to find which titles LT members actually like (after having read them) as opposed to simply owning them (with many books cataloged on LT possibly only being copies that their owners are still yet to read) is to look instead at the title's "average rating" (a score between 0 and 5 based on the cumulative star ratings for that title by LT members). When this approach is taken the 15 highest scoring AC titles are as follows:

1. And Then There Were None - 4.06
2. Murder on the Orient Express - 4.04
3. The Murder of Roger Ackroyd - 4.01
4. Death on the Nile - 3.89
13. Cards on the Table - 3.81

14. Sleeping Murder - 3.78
7. The Murder at the Vicarage - 3.76
6. The A.B.C. Murders - 3.75
23. Five Little Pigs - 3.75
11. A Murder is Announced - 3.72

19. The Moving Finger - 3.72
32. The Tuesday Club Murders - 3.72
5. The Mysterious Affair at Styles - 3.71
10. Curtain - 3.71
9. Evil Under the Sun - 3.70

The numbers on the left are the popularity ratings (based on total ownership) used in the first approach, while the popularity ratings (based on "average rating" scores) used in this new approach are given on the right. Using this new method the first four titles are the same as in the initial method, but then things start to look somewhat different. In particular, the following 3 popularly owned titles no longer make the list of the 15 most liked titles:

The Body in the Library - 2,367 copies, but "average rating" only 3.59
Cat Among the Pigeons - 1,965 copies, but "average rating" only 3.59
4.50 from Paddington - 1,827 copies, but "average rating" only 3.69

The 3 titles that replace them are shown in bold font. Personally, despite their obvious popularity,I don't think that the above 3 titles, nor 2 of the 3 that replaced them, belong on this list. So, to wrap things up and to provide yet a third approach, the following is my own personal choice of AC's 15 "must have" titles (having now read over 50 of her books):

Essential Poirot titles:
1. Death on the Nile
2. Cards on the Table
3. Mrs. McGinty's Dead
4. The Hollow
5. Murder on the Orient Express
6. The Murder of Roger Ackroyd
7. Murder in Mesopotamia
8. Lord Edgware Dies

Essential Marple titles:
1. A Murder is Announced
2. The Murder at the Vicarage
3. The Moving Finger
4. A Pocket Full of Rye

Essential titles not featuring Poirot or Marple:
1. And Then There Were None
2. Crooked House
3. Ordeal by Innocence (I believe this was AC's own personal favorite)

Titles in my list that are not on either of the first two lists are shown in bold font.

# 8 "Almost everyone who has responded so far here completely shirked this question and used his request simply as an excuse to post a list of their own few personal favorites."

I don't know about the others but I personally did not 'shirk' the question. If you are correct then I simply failed to understand the OP's question. As humans we are allowed to make mistakes, aren't we? :-)