The imperial navy fleet should be built around its workhorse, and this is the standard imperial navy cruiser. How the fleet will work thus will depends on the theme of the standard imperial cruisers. Imperial cruisers are defined with 6+ armored prow and short ranged but powerful broadsides. Thus the usual way to play imperial is to stick your fleet close together as you drive toward the enemy, secure behind the 6+ armored prow, shooting your nova cannons or torpedoes until you split and splinter their fleet with broadsides. Sticking together means the cruisers should work together, complement each other, and probably be squadroned. While it is quite reasonable to maintain a force apart from this thrust to harass and harry from afar, it would be unlikely to win engagements if most of your fleet plays this way. Most of the cruisers just do not have the range and both torpedoes and nova cannons are just not reliable enough at range to consistently win.
The Dictator = good. A combined bomber-torpedo attack works better than either alone. When both ordnances are combined into one ship this means just one reload roll is needed.
The Lunar = good. Best when squadroned with another lunar or two. The combined batteries will be supported by the combined lances that will be there when you need and want it.
The Gothic = average. The gothic comes with powerful lances but is best used as a supporting ship, letting other ships fire their batteries first.
The Dominator = average. Though 12 pts of broadsides looks great, in play against capital ships abeam you get only 4 dice, probably at 5+ to hit. Abeam because against a smart opponent they will want to cross your fleet as quickly as possible and thus won't let you fire on closing. Meanwhile, as previously stated, the nova cannon with the scatter die is unpredictable.
The Tyrant = better than average. The tyrant gets 10 pts of broadsides and against capital ships abeam this is also 4 dice to hit, just like the dominator. However, unlike the dominator it can fire its batteries to 45 cm ranges which will prove handy, and not just against Eldars. This slight increased range make up some of the short comings of the imperial cruiser format. For about the same points as the dominator imo it is the better ship.
The Dauntless = less than average. The dauntless lacks the 6+ prow of the standard cruisers, making it less survivable as the fleet moves forward toward the enemy. It also lacks the fire power of the standard cruiser or even an equivalent points of swords or firestorms. It is almost as maneuverable as escorts and slightly more durable. The only advantage of the dauntless is that being a cheap cruiser, it allows you to take a battlecruiser or a battleship sooner points wise.
I think all battlecruisers are average. The only advantages they offer are longer ranged batteries (but not much better than tyrants) and long ranged lances. Ranged batteries are really defensive fires and while long ranged lances are good, it is unlikely you can match the number of ranged lances other fleets can field. In addition, with the longer ranges, you might be tempted to play them separate from the main fleet. However, this will weaken your main thrust of more affordable cruisers spearhead.
The Emperor = above average. At 365 points it is the more expensive battleship. Going for it are 8 squadrons of attack crafts, including assault boats, up to 16 points of 60 cm batteries broadside (6 attacks at 30 cm against capital ships abeam and 3 attacks at 31-60 cm) or 10 points of 60 cm batteries forward (4 attacks at 30 cm against capital ships abeam and 2 attacks at 31-60 cm), and most valuable the +1 leadership. Against it are the 5+ prow and the 15 cm move that makes it vulnerable to not being able to turn if there is even just one blast marker in the way. Most would field the emperor apart from the main spearhead where it would be less effective.
The Retribution = above average. At 345 points it is the less expensive battleship. It has 12 points of 60 cm batteries broadside (4 attacks at 30 cm against capital ships abeam and 2 attacks at 31-60 cm) which is only slightly less than the Emperor but once you factor in the 3 lances and at over 30 cm ranges it will have more firepower. With the 6+ prow it will fit right in with your cruiser spearhead and thus be fighting at short range typically.
What escort to take really comes down to covering the deficits of the cruiser spearhead. If there are dauntlesses, you might not need them at all. If you are lance heavy with gothics, take Swords. If short on lances or relying on cruiser batteries broadsides then take Firestorms. Cobras should be taken with an emperor to get the attack craft-torpedoes synergy.
In general, an Imperial fleets should have many dictators and lunars, a few tyrants, some dauntlesses, and a battleship as your centerpiece. Such a fleet certainly won’t be a sure win but would be fluffly and reasonably competitive.