For me, Star Wars, City and Creator.

Star Wars got me out of my dark ages, and I have began buying City and Creator to bulk up my collection.

I am exactly the same. My collection is by far mostly Star Wars, but I really like the Creator and City themes.

Creator Expert

Collectable Minifigs

City

What an intriguing question indeed!

At first one would think the answer is simple. Later on with some more thought it's not that simple at all. Finally I ended up analyzing the question .

There have been some excellent themes named here already (like technic, star wars, friends, lotr ...), so I'd go more into why something counts as the best ...

I'd say there are 4 (at least) ways see legos

1) as a toy: main goal is to play with it and the building is just a means to an end

2) building: following instructions to the t and be happy once it's done

3) creation: make something without proper instructions and admire ones craftsmanship

4) collection: get all of something

and of course there would be a vast amount of variations within the named 4. Friends, Indy, LotR, PotC, etc. would be the best in this, depending on which movie is on . Star Wars and technic would fill the second category and Technic and creator the third. The last one is a bit tricky though ... but I'd go for minifigures.

Edited December 10, 201410 yr by Perza_FI

This is a tough question because their are aspects of all the themes that I have liked, but these are my persistant favorites:

1.) Technic - even though a majority of MOC are not Technic in style, I use many of these concepts in my MOC. It is still an all time favorite.

2.) Creator - From the modular houses to the simple cars, these are a favorite to learn new building techniques

Other themes that have influence my building....

City

Friends

Galaxy Squad

Monster Fighters

Chima (1st Wave)

Gotta go with Mixels. It's what really rekindled my interest in LEGO in general, and they come at a great price.

Adventures theme followed by SW and Indiana Jones.

Atlantis, Monster Fighters, and Galaxy Squad.

Those are my favorite ones. Creator Expert is another one also.

For me best are pirates and castle :)

Space and LOTR wasn't not bad too.

For me, it has to be the CMF series. Getting individual characters inspires a lot of very different MOCs. I have probably built more than 100 16x16 or 8x8 vignette MOCs based on characters in the CMF range.

Castle

Classic Space

I myself would probably say it would be chima and creator. Love the animals from Chima. Also like the modulars from creator.

Edited December 13, 201410 yr by LegoGuyK

The Castle theme, in all its incarnations.

But in the context of this question, is there a difference between "best" and "your favorite" theme?

Creators offered me the best bang for my bucks so it remained on my top preferred theme. Chima and Ninjago are fighting for my 2nd place and recently Mixels are hot on the 3rd place in my private leaderboard. Tides will turn depending on which theme offer most (ball)joints and hinges for my MOCing need.

Edited December 15, 201410 yr by alanyuppie

1. Technic

2. Creator (expert, modulars, all houses...)

3. Castle

4. Pirates

but frankly - all of it ;)

Technic :)

My favorite Lego theme is Friends.

I love how it has brought so many new customers to Lego. And so many of my mommy friends are now talking about Lego and wishing there had been Friends when they were little girls. Before this, I was kind of alone in my love of Lego.

Edited December 16, 201410 yr by Sarah

It used to be Classic Space specifically Blacktron, but nowadays I'd have to say trains, but ones MOC rather than the official sets, although I get them as well.

I think my vote goes to Creator, as I think it's the closest to Lego as it is meant to be. Relatively generic pieces and multiple models per set to show that one can indeed build everything. Also there is some detail, but not so much that nothing is left to the imagination anymore.

But Architecture is another really nice one, that shows people you can replicate all kinds of real-life architecture with the Lego system.

Lord of the Rings, there are always good space themes and sets, Star Wars, Guardians of the Galaxy, The Lego Movie even had a spaceship, spaceship, spaceship. Castles are a little harder to come by and LotR just has less competition.

Edited December 17, 201410 yr by BrickTamland

My favorite thems are Castle and Pirates and everything that can be fit into those two (such as LOTR, Hobbit and PoTC).

However, I think the "best" theme is the bigger Creator sets such as the modulars. They're simply masterfully done, and if I could afford to do so, I'd collect them all.

Excluding Licensed Themes and Evergreens:

Atlantis, Pharao's Quest, Monster Fighters, Agents, Alien Conquest imho.

For me it's Bionicle.

It has everything I like in adventure stories.

1) Heroica - endless mocing without having to have too many pieces. Like microscale, but more awesomer!

2) Blacktron, M Tron, Ice planet. Yeah. I'm a sucker for space.

3) CMFs

But best of all- though it's not strictly speaking a theme- but MONORAILS!!!!

I'm for City and Trains. I'm very partial to miniature versions of cities. If it wasn't LEGO, it would have been Hotwheels, Matchbox, and S scale or OO scale trains