Well, my best pulls by card category:

Baseball - Derek Jeter 1/1 "buyback" AU (1999 Topps Chrome) from Topps Archives ...not technically a "pull", as it was part of a very lucky random-team multi-box break

Basketball - some random European stiff's RC AU redemption card from Upper Deck that I mailed in, but they didn't have it, so it was substituted with a 2000-01 UD e-card of Penny Hardaway AU,GU,SN50

Football - Tom Brady's 2000 Pacific RC Platinum Blue foil parallel, pulled from a 3-pack hanger sold at Big Lots

Hockey - Mario Lemieux's 94-95 Pinnacle "Artist Proof" parallel, bought in a multi-pack/multi-card hanger at K-Mart for only $4.99, and the AP card was the one placed at the top of the stack for all to see!

Non-Sport - John Travolta (as "Terl") AU,SN300 from a 2000 UD "Battlefield Earth" movie card RETAIL box (bonus: the SN is "123")

Other sports - Brian Deegan's 2000 Press Pass Rage AU - not worth much & I pulled more than one, but when I went to sell them on ebay, expecting only a few bucks, a Metal Mulisha bidding war pushed both to $50 each, so in hindsight a great pull.

...most of my list is from the "turn of the century".  Newer packs & boxes with their "guaranteed" hits make those "great" pulls seem less significant now, than before - another "1/1"... yawn.

I'll expand it out to my other interests...

Pulled Christmas Day 2000. Only the second jersey card I had ever pulled. And the first one was earlier that day. from a hobby box. (The Gretzky posted earlier was also from a hobby box)

From a single pack purchase at the Target in Kingston NY sometime in late 2003. Although this is not the rarest or "best" card I've ever pulled, he is my absolute favorite athlete and this is my favorite pull ever. 

This was also a hobby box. This thread now contains 4 of my top 5 pulls of all time. The other is my 2nd Kobe autograph. Funny thing is that I had debated doing a Top 5 Pulls post on Cardboard History after I wrote my memorial post for Kobe and mentioned that they were two of my top 5. 

My best pull as far as valuable was last year - a Johnny bench autographed from the 2019 heritage real ones red set.  Somehow it was in a $20 blaster box from Walmart.  I sold it on eBay in less than 48 hours for about $285 if I recall.  I was happy with the turn around, even though I think some were even selling higher at the time.

https://www.tcdb.com/ViewCard.cfm/sid/198598/cid/12733713/2019-Topps-Heritage---Real-One-Autographs-Special-Edition-Red-Ink-ROA-JBE-Johnny-Bench?PageIndex=1

2018 Topps Update US250 Acuna white jersey batting SSP

This was by far my best pull. I got it from a hobby box I ripped from my LCS. I did contact them to see if he would take this card in exchange for some 50's Tigers I needed. They weren't interested. I did sell it to a fellow TCDB member who collects SP cards. I believe this card is now selling for 4x to 5x what I sold it for, but I have no regrets since I'm fairly sure the member still has this card and I'm glad i was able to help him out as he helped me out because I did use some of the cash to buy a couple vintage Tigers I needed.

https://www.tcdb.com/ViewCard.cfm/sid/175264/cid/11909591/2018-Topps-Update-US250-Ronald-Acuna-Jr.

Don't laugh but mine was a 1998 Pacific Paramount Cooperstown Bound Mark McGwire. It was in 1998 during the McGwire/Sosa homerun race so at the time it booked for $150, there's been a slight value drop since then.

Baseball - 1975 Topps George Brett RC

Basketball - 1986 Fleer Charles Barkley RC

Foorball - 1978 Topps Tony Dorsett Topps RC

Hockey - 1980-81 Topps Wayne Gretzky

Nascar - Jeff Burton Auto (I think it was Press Pass)

I'll have to break this down into "cards I still have" and "cards I immediately traded".

STILL HAVE:

MLB - 2009 UD Icons Immortal Lettermen - Ozzie Smith MANU SN40 (b/c that's exactly what I hoped to pull from the box)

NFL - 2000 UD Ultimate Victory - Tom Brady RC SN2000 (from a single $3 pack given to me for Xmas in 2000)

NASCAR - 2016 Panini Certified Signatures Spectrum Blue - Jimmie Johnson AU, SN15 (1st pack-pulled AU of him)

TRADED:

MLB - 2009 UD Icons - Pablo Sandoval RC, AU, SN100 (traded it for a NmMt 1979 Topps Ozzie Smith RC) Yes, it was from the same box as the Ozzie Lettermen card!

NFL - Probably 2008 Leaf Limited Slideshow Autographs - DeSean Jackson AU, SN50 (can't remember what I traded it for now)

NASCAR - 2010 Press Pass Legends Family Autographs - John Force and 3 daughters Quad AU, SN25 (most valuable BV card I've ever pulled @ $350 - traded for my 1st Johnson AU card that's also a MEM, SN48 AND a 2009 Showcase Mark Martin 3x MEM SN5 card)

NASCAR #2 - 2009 Press Pass Showcase Jumbo Swatches - Dale Earnhardt Sr. MEM, SN25 (BV $300 - traded it and several other cards for a Danica Patrick 2010 Showcase AU, MEM, SN25 AND a 2011 Showcase Jeff Gordon AU, MEM, SN45)

Besides the Brady RC, all the cards were pulled from a single hobby box. The Earnhardt was pulled in 2018, but the rest were pulled the year of the product or early the next year.

Bought some opened packs to fill in my sets from various years. 

Found a single 2011 Topps Update pack...  Pulled Trout's RC.

Here are a few decent ones.

1998 Leaf Rookies and Stars Longevity SN/50 Peyton Manning. Graded out at 9.5.

1999 Upper Deck Century Legends Epic Signatures #JU Johnny Unitas

1998 Bowman Chrome Golden Anniversary Refractors #127 Reggie White SN/5

I can narrow it down to two cards.  From the 1974 Topps. Card 386 & card 474. They were my two favorite cards, I pulled when I was 9 years old. Two great action shots of gameplay. Card 474 is of the World Series, Game 3. They are the cards that made me like action cards over just a posed photo.

Best, dose does not mean a high price. The best cards are gameplay. Action, frozen in time. 

I find it odd that so many say it's not about the money it's about the love of collecting. When the list is of higher-priced cards and some bosting & posting the price.