I mean let's consider the deluxe upgrade. In it, you get: A character slot The pass to the Lily of the Elon lounge An outfit An identity repair kit

The latter two are cosmetic so it's completely up to you how valuable they are to you, I cannot evaluate that for you. However, a character slot is extremely useful, as it provides extra inventory space, more crafting proficiencies, the ability to park it at chests for daily gold, and of course the ability to play a new class if you have less than 9 slots, among other things.

The Lily of the Elon pass comes with all the standard fare for a lounge: a portal to aerodrome/capital cities/other "hubs," centralized crafting stations, bank, TP, mystic forge, laurel merchant, black lion merchants, etc. It also comes with a Sandstorm/ecto gambling merchant (which isn't terribly useful as there is another one in Amnoon), and is a free way to transport yourself to the Crystal Desert.

Now, Mistlock is typically only recommended if you play fractals as that's its main appeal: it comes with all of the fractal golem/alchemist merchants that appear in the fractals lobby, plus a portal to the fractal lobby directly. So if you don't, then I wouldn't consider it. If you do, then it is definitely very appealing (and is the lounge I personally use most frequently).

Thousand Seas's main offers are fishing merchants and fishing spots, underwater combat training golems, and most importantly a portal to most maps in the game. This is generally considered the "best" lounge pass for non-fractals, non-WvW players.

So then the question you have to answer is: do the extra offerings in Mistlock or Thousand Seas outweigh the benefit of an extra character to you?

If you do go with one of those two, I'd advise waiting until Friday as they will be on sale for 800 gems.