I will agree that each KoF is worth owning, each has it's own charm. If you're used to the "New Neo" games which feel have more of the smooth movements and tournament feel, both 94 and 95 will be frustrating at first. Especially for me where King's moveset remained the same through the series but the actual input for those moves changed drastically in 96. B-QCD + P for a Double Strike blew my mind after being used to KoF 98's double QCF motion.
96 is a fun romp, nice atmosphere but a lot of people will hate on the 'extra' system. Basically whenever you get hit BAM super meter is at full, and you can do a DM. When the time runs out, next time you get hit... that's right you have a DM at your disposal again. Still, this doesn't hurt the gameplay for me as DMs don't get used nearly as frequently as they're available so I enjoy it.
97 is my absolute favorite. The storyline picks up from 96 very well, great gameplay engine... everything is smooth as silk. I love the 'Satella' stylings, finally giving KoF the tournament feel it seemed to really lack in other games. You'll see what I mean. It seems to be a bit hard to find lately on MVS but it's not getting overpriced due to that. That's a good thing
98 you already know and love, no need to spend time on it
99 is.. well it's pretty good audio-visually. The striker system takes getting used to but overall it's not a bad game. Probably my least favorite but that didn't stop me from putting it in the PSX kiosk at work and playing it when I was at Gamestop
2000 is my favorite of the striker series but then again I've yet to put a lot of time in 2k1. 2000 isn't that balanced but it's one of those 'just damn fun to play' fighters. It doesn't seem to matter that the strikers are overpowered or some characters are god tier. It's just fun to tool around with. I love the graphic style in this one too.
2k1 - Ugly but deep. That's all I can say about it now.
2k2 - Not much time into this one either, but it's another dreammatch like 98. NO King though

But I can see where the "most balanced KoF" line comes in with this. Bleh on graphics, BIG on gameplay which is where it counts.
2k3 - The start of something new. I love 2k3 personally even with all it's flaws and glitches. The tag system is the start of something beautiful but I will go along with other posters in saying to play others first before this one. Especially with the storyline going into this one, knowledge of KoF history is a must for this
that's my take on the series!
-AG