Personally I've had a few so far and had to let one go stupidly(Tetris) which I want back...figures it's out of print and costly.
I've currently got Picross DS which has some insane play time involved and added fun with a lot of downloadables too. This one is your classic nonogram grid game where you figure out in something similar to minesweeper just exactly how to pop the right stuff to make a picture for the theme of the area. Things start small from I think it was 15x15 and get up to I believe 25x20 which is damn hard. This game has a good 100hours of play going for it at least unless you're just some nonogram math god who can do it in a good deal less, but at $20 who's complaining?
Planet Puzzle League I had and it bored the crap out of me so I sold it as it just did nothing of value new other than being itself, which I was more burned out on than I thought. The game just is what it is from the past variations minus the insipid pokemon the N64 copy had or Yoshi on the SNES/GB, and at $35 was overpriced.
Zookeeper is a great game and unique, was horribly 2x over overpriced ($40) at launch and hit reasonable ($20) too late to do any good, but it's damn good. You can only slide one piece and just once, have to clear out X amount of so many animals on each board. You can earn a few cheat binoculars to see moves you're blind about, and also has some varying modes on top of an odd quest game.
Tetris DS is kind of self explanatory, but it does have some odd new modes where you can touch the screen to drop stuff which is kind of good, and a push mode where you get into a tetris block shoving match, and of course classic. The game I got sick of because you could easily roll it over as you never had to settle for a piece drop (roll the crap out of it so it never settles, then hit NEXT to pop switch it out if you need to.) I miss it though, thinking of a re-acquiring of it. Sadly used/new whatever you're looking at $35-40+ for a formerly $30 game.
Meteos is another on the market but it's really a hit or miss thing with people. Fully intended as a stylus type game you just slash the screen to line up so many pieces to make them hopefully rocket off (and clear) from the top of the screen. The issue with this game is that you technically can for a long time just slash the crap out of the screen and eventually clear a lot of stuff setting some fine records. Game does track everything and you can buy new stuff with those collected pieces you clear, but ultimately it does wear really thin after time. I just recently got rid of it as it just wasn't cutting it anymore (and used the cash towards Space Invaders Extreme DS and Arkanoid DS.) This game can be had dirt cheap these days in used $10 bins so if its your deal go for it.
Prof Layton games are there, but they're very hit and miss depending on your tastes. These are NOT puzzles by 'classic gaming' terms (like Tetris, Puyo, etc) but brain teasers and if you hate them the awesome cartoon cover story and visuals won't save it for long, but if you love quirky mind benders each one had over 100 in it to mess with.
Puyo Puyo which I popped just above is another that came out but didn't have a huge run or following at least on DS so finding it probably wouldn't be too hard for a fair price. It's your classic 'kirby avalance/mean bean machine' clear so many of the same color type thing sorta like Columns. This game here is a huge favorite among many(Puyo) and has a rabid fan following so it could be your best too. I've seen this I think around $10-15used and $20 new when I do see it pop up so the price is good.
Many of these really do deserve a 'best' status and those I listed all I think do depending on someones personal tastes. There are a lot of puzzles on the system, but these are the quickest that came to mind.
Since we got into 'best' stuff I left out the shovelware things that flash games are made of, though Zookeeper semi-qualified for that as that is where it started, but added so much content, upgrades, and added stuff it stands well.
