I am an avid ATK player so let me give you my two cents while addressing your questions in some semblance of order.
First, if you didn't know, the ATKs were introduced in the early 90s (1993 if i recall correctly) as Ibanez' answer to the then ubiquitous Stingray. You have to cast your mind back to the time as many prominent bass players were playing Rays- Flea, Joe Lally, Paul Barker, Tim Commerford, etc. So Ibanez wanted in.
But whether they intended to or not, they kinda hit the ball out of the park. IMO they created their best bass ever.
There were originally two lines of ATK basses. The USA made USATK was made by Dave Bunker in the USA custom shop and featured his patented tension free neck. Then 300 series was the production model made in Korea. Both were available in 4 or 5 string version though there were not many USATK 5s made.
The production models were called the ATK300 (4 string) and the ATK 305 (5 string). They were discontinued in the US around 1999 (they continued to thrive in Japan and even came out with new models with the 400 series which featured an added S pickup in the neck position) and then they were reintroduced in 2005 IIRC, made in Indonesia and featured the MM style truss rod spoke wheet adjustment. The reintroduction of the ATK around this time was likely to compete with the popular Music OLP Music Man models that were capturing the lower price point market for MM style basses.
Around 2011, they rebooted the 300 series and came out with the 200, 800 and premier 1200 series. These featured reimagined electronics (both PU and preamp) and featured a slimmer headstock design.
Where Ibanez really succeeded with the ATK IMO was they not only achieved a Stingray-esque sound, but they made something of their own that did some things the Stingray could not do.
For starters, there is a 3 way "character switch" which gets some variety out of the the pickup in addition to what comes from the preamp. They also designed the bass so that you could string through the bridge or the body. Remember that in those days, Music Man had not made a string through bass since 1982.
Lastly, between the giant metal bridge and the bass just not being a Stingray, it didn't suffer from the quiet G string problem many Stingray owners experience.
As for the pecking order, there is some subjectivity here but to me, the USATKs are pretty sweet but they feel different than the production models. Necks are heavier and thinner, and they play differently. A smoother more even response vs the production models which have a lot of punch and grunt in the sound.
If you are going to go with a production model (they are much easier to find) I would recommend the 300 series. And in general you cannot go wrong with the 300s. In many ways I think they sound better than the USATKs, they just feel a little different. The newer 200 and 800 series (as well as the 1200) are different basses to me given the redesigned electronics. The way I describe the difference between the newer ones and the 300 series is that the newer ATKs had the electronics re-voiced to sound more refined, like a clean and present boutique bass, whereas the ATK300s are just patently impolite. I prefer patenetly impolite.
Also, I have no preference between the Indonesian and Korean 300 basses. Both are great. The Korean ones tend to have nicer necks but not all the time. The Indonesian ones are every bit the same quality and the truss rod spoke wheel is pretty convenient. And once in a while you can find the Indonesian ones in some pretty cool colors that they were just not making in Korea.
If you opt for the 5 string, I think the B strings are thunderous. And the string spacing, while tighter than on the 4 string, is very comfortable and allows for easy playability. If I had to guess I would say 17.5MM jsut like the SR5, and the ATK300 would probably be the same 19mm as the SR4.
I don't think this bass will sound vintage per se, but there is plenty of growl and grunt. You can get close to that Jaco burpy back pickup sound if you want but that is not really what this is for. It's more likely to sound like a J when you have both PUs dimed and you are digging in to make the bass growl with your hands.
I have owned many ATKs over the years, with my olderst one being a 1994 and its like new. Rock solid axe. Made well, great electronics, no complaints by me.
As for strings, I enjoy DR Hibeams and Sunbeams. Brings the growl out.
I have to say I love these basses. I also own several MM Stingrays and some Warwick MM style basses. Each does the MM thing a little differently.
But if this sways you, last year, my college band was asked to play out 20th reunion. We were kind of a big deal back then and when they announced we were playing reunion attendance shot up to where we broke a record. So we were playing for a 400+ crowd on a proper stage with proper sound. Stakes were high so I auditioned my 5 strings all summer to find the best bass for the gig and my number one pick for the gig hands down was an Indonesian ATK305. However, it felt odd taking a $350 bass to such a gig so I took my USATK5. My backup was a MM USA SUB5.
The USATK killed. I played through a GK MB212 and the tone was monstrous. I had intended originally to play the SUB5 on certain songs where the timbre of that bass worked a little better but the ATK sounded so great, and was so comfortable to play (including all day the prior day for an 11 hr rehearsal!) that I could not put it down.
So yeah, run to the internets, don't walk, and get yourself and ATK!
