I don't RO often, but when I do I prefer RetRO
Stability -It's more stable than Francium... I'm not sure what else to put here. I don't experience any lag that I can attribute to RetRO. With assumed routine maintenance and server local, I am pretty sure that RetRO provides an excellent connection to most all. Perhaps a goof in scripting or an act of shenanigans may cause brief periods of lag, but I think this is rare and I have yet to experience it.
Class Balance/WoE -It's got more balance than a tightrope artist. If the basic fact that thara and possible poo poo hat are about the only redux you need for WoE/PvP, to begin to get competitive, hasn't registered yet from reading other reviews, then this reiteration was warranted. Due to pretrans, patch period, etc, gear dependencies and selection are minimized (for the best imo) to an extent that I can do well with +4 gears (overupped npc gears was also an option for me on at least swordie classes). As also stated, a pvp match or woe battle is scaled by said measures and most often results in an obtuse and epic fight.
Economy -RetRO succeeded where American automakers failed! With the server's aging nature, a healthy economy is served up to both new and old players alike. Dedicated RetRO players have a general consensus of base prices for many items, and it does not take long for the new player to become accustomed to popular items' values. The market values are also, in this writers opinion, quite friendly for the new player looking to buy that piece of slotted gear they can't get to drop. An avid entrepreneur should have no problem getting established in the market, and the average buyer/seller shouldn't have much problem either. Values, even with bases associated with them, usually reflect a margin of over or under pricing, but it would seem to be rare that the margin is huge (I don't often see items marked up 2-10x of what they are actually worth).
GMs -They are around! I am a personal fan of the non-intrusive nature of the GM team. I like knowing that bots get busted, and yet on the rare occasion that I am checked for botting, the process is quick, to the point, and it's as if it never happened after it's done. The team as a whole seems to be highly professional in how they approach the business of operating and moderating the server. While methodology can be argued at times, those debates, when they are within reason, are most certainly listened to openly by the team, approached logically, and more often than not resolved in a manor that keeps both team and players alike happy. I can't prove it, but I think the RetRO GM team might have surpassed puberty.
Server -I got served... an excellent, polished, refined, aged, dedicated, antiquated, professional slice of RO when I first signed up at RetRO, and I haven't looked back. I was given the keys to a simpler time where, with no warpra, job changer, platinum skill npc, etc, I had reason to walk from town to town, to hunt on obscure maps, to adventure! WoE became epic, pvp matches lasted more than a second, tactics from the past became daily staple. It went beyond nostalgia for me; it was exactly what I'd been looking for.