Mine was MGT-01 "Delicate Warrior" Arcee. I was so impressed that it actually got me back into collecting Transformers, as I had not bought any for a considerable time, and now I'm buying 3P stuff as often as official stuff.
She's still my favourite 3P Transformer, so I just had to get the more recent Blue (Chromia) and Green (Paradron Medic) versions as well.
I won't be getting rid of any of them either.

 

My first third-party purchase was the G2 Boosticus Upgrade Kit some years ago, the kit is somewhere in storage with 4/5's of FoC Bruticus.
My first figure purchase was Microblaze's FoC Onslaght about 10 months ago, and I still own it.

 

My first 3P purchase was back in 2000. The Beast Machines add on kit from Unicron.com. A lot of people forget about them. Really, to me, they are the "originators" of the 3P add on kit.

- Gregg

 

I steered clear of 3P stuff for a looong time. I was very ignorant of what I was missing out on. Until the fateful day I saw a Fans Toys Sever for under $150 and figured what the hell. Well that wowed me so much that it opened my eyes paved the way for Buzzing, Reximus, G2 Scoria, MPP-10 and Chrome Guttur so far. Eligos and Stomp on pre-order and once I get refunded for my first purchase I got scammed on and if I can find a legitimate and ethical seller I'll have MPP-10b Nemesis as well.

 

FP Protector armor. I really do still like the look of it but I've contemplated about getting rid of it along with the rest of my classics collection to make room for MP. This scale just had so many great 3P and retail releases I'm just struggling to let go. I may just keep a core set of exceptional figures and sell the rest  

 

Maketoys giant. He was awesome and I loved him but I got rid of all my classics stuff to make room for masterpiece. He looked great with some classics seekers to hang out with but I got rid of all mine.

 

warbotron brawl and swindle

been chasing the dragon ever since

 

FP G3 trailer. Still have it, though TW Orion has inherited it from Classics Prime.

 

Ollie. Pretty terrible introduction to 3P, but I still have him. I like Wheelie a lot actually, I think he's cute.

 

My first 3P was PE Warden, which my wife bought for me at my first BotCon. I thought she got lost, and the next thing I knew she was shoving it in my face, thrilled to have found something she knew 100% I did not have in my collection. He's currently hanging out in my display case next to the other 3P headmasters in my collection.

 

MP-01 Masterpiece Trailer Third Party Accessory Review - Transformers News Reviews Movies Comics and Toys

This trailer was my first. I no longer have it.

 

D'oh. Do the fixes. Super easy and you'll have a pretty darn decent figure!  


My first 3P purchase was Quakewave. Which I bought almost instantly after being reintroduced into this fandom. No coxing or or advice made me do it - I was a 3P fan from the getgo  

Do I still own him? Yeah but he's boxed up.

 

Quakewave. Yes I still have it, and yes it is still my favorite.

 

My first was Fansproject Ultra Magnus, and I definitely still have him with my other season 3 Classics figures. People can say what they want, I still choose him over any other rendition of Ultra Magnus.

 

I gear Shark Attack Squad. Still have it, may buy another set because, well, Shartikons man!

 

Quakewave. Still have him.

 

FansProject Colossus set Munitioner and Explorer. Finally sold them last year.

 

KFC Transistor. Still have him, though I debated the pure red one for a bit. All-in-all, I think I like the metallic one more.

 

Fansproject Insecticons. Loooooong gone.

 

I got the MP-1 Trailer from Just Toys way back when the 20th anniversary Prime came out. I guess that was first.

The first real figure was Scoria from Fans Toys because I wanted all the dinobots to go with the MP Grimlock. I had no idea what that would lead to.

Still have both.