I don't know enough to suggest a ranking of the different crosswords, but could suggest that the Daily Telegraph cryptic might be a good one to start with. I think it has a wide and active following, although I do confess that I don't do it myself.
A step up (in terms of hardness) would probably be The Times daily cryptic crossword.
Of course, if you already take a regular newspaper, the cost of taking another just to do the crossword might be a consideration.
Most of the big newspapers have websites archives of their crosswords available for free. You could look at some of these to get a feel of what they offer and the level of difficulty that you are prepared to work at.
Good luck - and good enjoyment of course, whichever way that you go!