While some factors like crew comfort are unlikely to vary much over time, most of them are a moving target. The S of the Excelsior when it launched is a B today, for example. The A of a refit NX-class is a D today.
D is a disaster in that area. Half the ship wants to fly apart at the seams, sourcing materials for it is difficult or there's zero overlap in existing production, the phasers couldn't tickle a fly, it can barely tell you anything about something until you're right next to it, the crew are in bunks and even the captain lives in a broom closet.
C is below average. It's fiddly and temperamental to maintain or produce, the weapons are serviceable but really shouldn't go up against anything designed to fire back, it can perform science semi-competently but you won't be making any breakthroughs. The officers have decent quarters, everyone else has bunks.
B is middle-of-the-road. Whatever that category is, the ship can pull its weight. It isn't difficult to keep running, it isn't difficult to build. It can take a hit and shoot back. It can do some innovative science if it finds something sufficiently interesting. The crew have rooms to do more than sleep in.
A is high-end. The ship runs like a dream, or it's very easy to produce in bulk. Other powers would probably say it has the armaments of warship. It has systems modern enough to do some cutting-edge science, and plenty of options to choose from. The crew has their own individual rooms.
S is as good as it could possibly be. The ship could sit abandoned in space for fifty years and start running again when you press the power button. Starfleet can pump them out as fast as Naussican can lose at dom-jot. It doesn't have the weapons of a warship, it is a warship and can give anyone else a run for their money. It has a vast array of scientific instruments that can catalogue everything under the sun and probably enough experts enticed to work there to write a thesis or two on their findings while on the job. The crew all have officer-grade rooms with private amenities like sonic showers and personal replicators.
The Sovereign-class would probably be a B-C-S-B-B. Not much more highly scoring than the Renaissance and worse in the ease of production category. But it's a damn good combat ship and that's what she was mainly designed to do. Meanwhile the Galaxy would definitely have an S in comfort and science, but it might rate a D in ease of production or a C in maintenance.