Snipe-B Battle Frigate (SNB 75 bpv): This is the same old Snipe you know and love, but with another plasma, 2 more ph-3, and more energy (9 total). Still the power troubles. You can get better frigates for about the same BPV, and there's good stuff on the market in Middle era so you have no excuse. Unless you have a fetish for the Old Series, take another ship.

KR E4 Escort (K4R 64): The E4 conversion is pretty good. Because of the Plasma F's no holding cost, after you arm them you can go fast in this ship, faster than most other frigates. Like most earlier Klingon ships, you get really bad rear shields though.

KR E4 Escort Refit (K4RB 68): This is the same ship, but the shields are fixed. Take this instead of the K4R if you can.

KR F5 Frigate Refit (K5RB 85): Fortunately, the shields are increased on the original K5R, and you get the K5RB ship. It's a good frigate.

KR F5 Frigate Leader (K5L 104): If you're looking for a Destroyer, it's either this or the Skyhawk. It's just which one you like better. The Skyhawk has lower-cost weapons and is faster but the K5L has long-range Plasma-Gs.

Skyhawk-A War Destroyer (SKA 102): The Skyhawk is a great ship. Like most New-series ships, it's very energy efficient, and has good maneuvering and shields. You'll also notice that compared to earlier ships, the plasma arcs are split, so with just a little turn, you can almost fire them backwards. This is perfect for Ballet.

Sparrowhawk-A Light/War Cruiser (SPA 125): The SPA is also a fast, fast thing. Good choice for a light cruiser. You can go 31.0 while charging all of your plasmas. That speaks for itself...

King Eagle Command Cruiser (KE 140): This is what happens when they upgrade the WE. It adds 2 Pl-F and lots of power. You also now have triple-green (30) on all 6 shields. This ship shows that the Old-series ships can still be dangerous in the Middle Era with these refits. The KE has the power to move at a decent pace, but I still think it's made for the old cloak tactics.

KR D6 Cruiser Refit (KRB 132): The KRB is the KR with better shields, and the Pl-G are upped to Pl-S's. The original KR was pretty good, and this refit solves its weaknesses and gives it more firepower. Good choice for a light cruiser.

KR D7 Cruiser (K7R 151): This is the conversion of the Klingon D7. It is basically the KR with 2 more ph-2, 2 added pl-F, and 2 more power. It's a good ship, but you might as well just get the...

KR D7 Cruiser Refit (K7RB 166): K7RB, which adds actual shields to the back, and upgrades the plasma G's to S's.

KR D7C Cruiser (KRC 171): This is the conversion of the Klingon D7C. Now the D7C was a Klingon ship that actually had good shields, so this Romulan version does too without needing a refit. This ship is unique because it carries 2 Pl-D's.
In the middle era, the KRC and K7RB are the best cruisers and are about equal, so when you pick one it depends whether you want the power of the Plasma-S's of the K7RB or the defense of the KRC's Plasma-D's.

Condor Dreadnought (CON 234): Yes, there are Old-series dreadnoughts that come out before the New-series Condor, but you don't want them :). The Condor is pretty powerful compared to other races Middle era DNs. It has a lot of energy, so this is one Dreadnought which you can actually go very fast and charge your heavies. Yeah you guessed it: Plasma Ballet.