A dictionary makes a great present for someone who does crossword puzzles, reads a lot or who just loves words. Most households have at least one dictionary, but even so, dictionaries get out of date very quickly so I would advise people to buy a new one every five years or so.
We talk about looking something up in the dictionary, as if there were only one, but there are lots of different dictionaries and they vary enormously. Before you set off to the bookshop to buy a new dictionary, you should do a bit of preparation. What do you (or Auntie Maud, Cousin Fred or whoever you're buying for) want to use the dictionary for? Will you mostly be checking how to spell words? Do you read 18th- and 19th-century literature and want to understand unfamiliar words you come across? Do you need help when solving crossword puzzles? All dictionaries will do those jobs, although a very small dictionary may not be large enough to contain obsolete or archaic literary words or obscure words found in difficult general knowledge puzzles.
You may be hoping to improve your vocabulary and mastery of English from a dictionary, in which case you should be looking for one that gives example sentences, using the words in context, so you know how to use them correctly. Say you're not sure how to use the noun substitute in a sentence. Collins Dictionary gives this very thorough definition: "a person or thing that serves in place of another, such as a player in a game who takes the place of an injured colleague". Oxford Dictionary of English (ODE) gives a slightly shorter definition, but, unlike Collins it also gives a sentence showing that you need to follow substitute by the preposition for: "a person or thing acting or serving in place of another: soya milk is used as a substitute for dairy milk". The one-volume Oxford Dictionary of English, which has just over 2000 pages, is a very good dictionary for someone who's shaky on correct usage, perhaps someone who does creative writing and wants to make sure that what they write is correct.
Collins is a very good dictionary, too, although its spelling of some words is quite different from dictionaries published by Oxford. Collins says chamomile is a variant spelling of camomile, whilst ODE says that camomile is a variant spelling of chamomile. The English language allows for variant spellings, so you need to choose the dictionary whose variants you feel most comfortable with.
Prepare a list of words to take with you to the bookshop and then look up those words and compare their treatment in several different dictionaries. On the list should be words you know very well, specialised words from your professional field or relating to a hobby, some up-to-date words eg iconic, edgy and some slang. You will undoubtedly find differences in the language used in definitions. Some dictionaries may not have up-to-date definitions. Some dictionaries are more technical than others. Here is the definition of lily from three respected dictionaries:
ODE: a bulbous plant with large trumpet-shaped, typically fragrant, flowers on a tall, slender stem. Lilies have long been cultivated, some kinds being of symbolic importance and some used in perfumery.
Collins: any liliaceous perennial plant of the N temperate genus Lilium, such as the Turk's-cap lily and tiger lily, having scaly bulbs and showy typically pendulous flowers.
Chambers: any plant or flower of the genus Lilium, typical genus of Liliaceae, a family of monocotyledons differing from rushes chiefly in the large conspicuous flowers.
As you see, three very different styles of definition. There's nothing wrong with any of them; they are just intended for different audiences and pitched at different levels of knowledge.
When it comes to choosing a dictionary "you pays your money and you takes your choice", as the saying goes.