This phenomenon is quite extensive and encompasses not only Android ROMs but also Linux distributions and so forth. Nevertheless, in this post we will focus solely on Android ROMs and how you can find the one which suits you best among the vast proposed selection.
Finding the Right ROM for YOU
In order to do so, you may use the following comparison database made by XDA senior member nimrodity, who, in addition also bothered to keep it editable in case you have anything else to add, so feel free to ask for permission to join the database maintainers.
1) Now that you have the data laid right in front of you, it would be much easier to narrow the possibilities down, and choose only a ROM that has the set of features you are looking for, e.g. if it is most important for you that your chosen ROM would have a “multi-window” UI, then you can go with either OmniROM, Revolt or Dirty Unicorns as your favorite one.
2) Of course having the raw database in front of your eyes is a major boost that gives you some direction, but as life taught us all, there is more to it than meets the eye – so another thing you should take into account before choosing your ROM is: as a rule of thumb, the closer the ROM is to the source code thus it’s deemed to be more stable, the reasons for this are varied, suffice it to say that the more you change the more you are prone for errors, think about it.
3) Another important advice you should consider, which is not reflected by the database comparison is that all of the above ROMs are more or less having similar appearance with mostly the same default apps, all of the above but one – MIUI – is the only one who also brings a myriad of theme selection and a default iPhone-like look and feel out-of-the-box, hence, if you are fond of the way iPhone looks and feel, but also prefer taking advantage of the open source attributes, then MIUI just might be what you are looking for.
4) Last but not least, above all other suggestions, make sure your device is supported by your chosen ROM, otherwise, trying to install an unfitting ROM might end up with you having bricked your device, and no warranty could save you in that scenario, since most (if not all) companies sees ROM changing as a void of warranty, so be careful.
Good luck finding your favorite ROM :-)