so what way works for you?
The best way to study TACTICS

Is CT-art still considered a good tactics trainer? I've got a book from about 10 years ago here that tells how to use it to improve your game.
Good question! the way I study tactics is keep going over the same set until I can do the whole set quickly. Pattern recognition! The other tactic servers won't let you do the same set over and over. But every chess player do not go over a set several times. Most players just study different problems daily and do other studies like read material , master games, ect. What I'm starting to realize is just make your chess study easy as possible and just because one method work for one player make not work for another.

How is it different than something like the tactics trainer here or Chess Tempo?
CT-ART is structured training. Tactics Trainer or Chesstempo are unstructured, random problems. CT-ART teaches you ideas and builds on them. It's a much better way to learn.
The difference is "learn" vs. "practice." CT-ART is like the first half of the math class where the teacher shows you how to do something by building off of what he taught you before. TT/CT is like the second half of the class/homework where you practice doing what you were taught.

If one plays mostly blitz, then pattern recognition is very important. If it helps you to memorize certain patterns so that you can play them by instinct...then "more power to you".
I play only slower games, the old fashioned way. This kind of game means that calculation is paramount. There are virtually infinite permutations and combinations of patterns. With more time, there is more time to calculate. So when I do tactics, I do it without the blitz clock and I don't care to do it in sets. I also don't care to memorize...just to understand the calculation.
Of course, after playing chess for many years I also see certain combinations instantly. I consider that a bonus.
I wrote this post to emphasize that chess is not just about memory. Thinking is also very important. Or, at least it used to be.

Another thought...
I use the TT here and Chess Tempo, too. Here is something else that many may not be aware of. It is a free download and I train with it a lot on my Android tablet.
Take a look. I like it a lot: Tactic Trainer at the Google Store

Playing guess the move where the game may or may not have a tactic. Not just master games but also amateur games are good for this purpose:
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White wants to tie the queen to the defense of the b-pawn after moving the knight while preparing f4. Can I allow this plan and still be better off? 1…h6 is a candidate but don’t want to give white a lever to play against. My first candidate is …Nf8 since it unblocks the Be7 in case of e5. 1…Nf8 2.f4,Rad8 The Be7 is defended in case white plays e5, he’ll likely play f5 so e5 is forced therefore taking my planned …d5 off the table or at least give it less punch as the e-pawn would be somewhat loose. Wait, 1…Nf8 2.f4,Nxe4 simply loses a pawn, a big uphill battle for white. 1…Nf8 2.Rad1,Rad8 so far the primary variation.
If I find nothing better then Nf8 is my move. I really want to activate my queen’s rook but don’t want to waste a move moving it elsewhere. 1…Rac8 can’t find a plan here 1…Qc5 2.f4 doesn’t help me. Wait 1…Qc5 2.f4,e5 3.Nf3,Qxf2 4.Rxf2 he doubles on the f-file and has good pressure against the e5 point and I can’t play …d5 anymore. I want better than this. 1…Nf8 with flexibility, defending the Be7, prepares Ng6 and Rad8 push clock.
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I don’t like this move, Nxb3 encourages white to capture away from the center giving me structural superiority. 1…Nc5 didn’t do much compared to 1...Ne5 but seems like an acceptable enough move. Does Nxb3 contain a trap? It opens the c-file for white, but the Nc3 will need to move and it’s a horrible piece as it is, Nd1 would disconnect the rooks until Ne3 I may improve my position slightly if he moves back, after all is said and done can he make use of the file? 1…Nxb3 2.cxb3,Qc5 3.Qxc5,bxc5 with a superior structure, maybe 3…dxc5 instead? If 4…d5 after 3...bxc5 then exd5 and the isolated pawn pair coordinates nicely for a potential passed pawn.
1…Nxb3 2.cxb3,Qc5 3.Be3 drops the pawn. 1…Nxb3 2.cxb3 what now? 2…d5 3.e5,Qxe5 4.Qxb6 no, I don’t like that either, his threat against my bishop and control over many of my home squares trumps my centralized queen. 1…Nxb3 2.cxb3 any safe move? Back to …d5: 2…d5 3.e5,Nfd7 4.Bxe7,Rxe7 I can double rooks but I’m otherwise clumsily placed. I’m lower on space so recoordinating shouldn’t be an issue, the onus is on him to coordinate to transform his space into a real advantage.
1…Nxb3 2.cxb3,Qb8 with the idea of Qa8 is my primary variation so far. Still, the c-file and potential tactics seem useful for white. Anything else? So much pressure against e4:
1…Nfxe4 and a recapture would substitute one knight for the other also with an attack against the queen thus white has very limited options while exposing the Bg5 to attack, this could work:
1…Nfxe4 2.fxe4,Bxg5 with a commanding advantage.
1…Nfxe4 2.Nxe4 defends the bishop 2…Nxe4 removal of the guard, due to the threat against the queen Bxe7 isn’t possible thus simplifying the combination’s calculation. 1…Nfxe4 2.Nxe4,Nxe4 3.fxe4,Bxg5 is my new primary variation, white has an isolated e-pawn and weak dark squares whereas I maintain my darksquared bishop, initiative due to the threat against the Rc1, and central pawn superiorty and I can’t find a refutation so 1...Nfxe4 push clock.
Also CT-ART 5.0 because it's a very nice package deal.

Your post doesn't show anything for us to look at.
I did post the link. Then I found that it went to my personal account. So I deleted it. Go to the Google Store and enter Tactic Trainer.

Lucas Chess has several really good Guess-the-move modes, if you like that sort of thing.
Play Like a Grandmaster where you pick the GM you want to play as and can even narrow it down to specific openings. There's also FICS-Elo and FIDE-Elo where you play as weaker players and try to score better than they did via Guess-the-move.
I have 3 ways im studying tactics and i would love your opinion of which way is best. 1. computer with ct-art 4.o, 2. books , and 3. chess tempo on my phone. after reading rapidchess improvement i bought ct-art but i only have very small time to do my study on my computer. i really like ct-art but i wish i could download it on a tablet but that wont work. good books are so hard to find.