As a long-time GM and occasional player of Rogue Trader, I've spent a lot of time building voidships for myself, with players or to use against them. I've noticed over the years that I tend to do so with a very specific concept in mind. Essentially, I have discovered that there are 3 ways to build a gunboat (so-called because it is primarily a combat vessel vs. a ship with as much investment in utility components as armament).
Below, I'll list off my design philosophies with brief explanation/description of each. Thereafter, I'd like to know what some of you think. To narrow a mentality? Outright disagree?
Brawler: These warships generally prefer to engage at short to medium range with weapons that trade range for higher damage potential and strength rating. Crit is of secondary importance here because the brawler is going to outlast its opponent. Weapons like Meltacannons or Ryza-patterns are excellent choices here. An excellent choice for Cruisers, but dangerous amongst larger vessels because a Brawler caught overextended simply doesn't have the speed to disengage or the ram and lacks the armour to stand up to concentrated fire from multiple targets. Nonetheless, the Brawler is the simplest and most consistent of warships design concepts, not requiring significant modification and likely to perform well in nearly any situation. A light cruiser cannot function as a Brawler, it just won't last. Finally, a Brawler, while certainly able to benefit from escorts, is not dependent upon them for survival. Rather, the escorts merely serve as the mosquito fleet which the adept Brawler captain/commodore will use to bleed its targets in preparation for the killing blow.
Sniper: Built around long-range macrocannons and lance weapons, the sniper is designed to engage at extended ranges, where opponents cannot reliably return fire (i.e. penalties to BS due to range). Damage, strength and even crit rating are of nominal importance as even the most adept Arch-Militant is unlikely to score more than a pair of hits with each volley absent an exceptional roll. To the end, weapons such as Hecutor-pattern plasma batteries and Sunsears are perfect choices, along with extended range lance weapons. The sniper concept is where vessels like Battlecruiser and Grand Cruisers can shine. Lacking the speed to close on targets, but possessing the ability to deliver massive volleys from either broadside, the super-capital built as a sniper can lay waste to targets before they have much of a chance to close into weapons range, although a Cruiser can function servicably in this role. A Light Cruiser CAN excel here, but it must be an immensely fast vessel with a crack crew capable of maintaining distance and striking targets while moving at those speeds. Even when facing Cruiser sized vessels built in a similar fashion, this vessel can outlast and outgun its opponent(s). Finally, the Sniper, while able to begin delivering damage at extreme range, is quite vulnerable to small, fast vessels that can close the distance and avoid incoming fire - such as the Dauntless or Cobra. For the reason, an escort cadre is a near-requirement.
Wolf: Built around a combination of speed and high-alpha damage, the Wolf is designed as a cap-ship-killer. The Wolf will favor high strength and crit ratings and use macrocannons almost exclusively as the salvos from these weapons can penetrate the thick armour and heavy void shielding of capital vessels. Weapons such as Stygies-pattern macrocannons and Sunsears (broadsides, specifically) will serve as the Wolf's fangs, capable of crippling targets in a single broadside. These weapons, when fired in salvo, can punch through the thickest of armour. A Light Cruiser, while certainly possessing the speed to serve in the role, lacks the armour and damage-capacity to safely perform this role. As such, it must be fitted with components specifically designed to remedy these shortcomings. A cruiser, while certainly bringing the necessary firepower and armour, simply lacks the necessary closing speed - requiring similar investment and modification. Notwithstanding the apparent strength of the Wolf, it is nearly impossible to properly build and crew as few hulls provide a good base, therefore requiring a significant investment of SP/PF in order to properly construct a vessel whose role can be filled by a pair or trio of cheaper escorts. To that end, the Wolf, if properly build, can function well as a member of a fleet (the super-escort role) or even as the true lone wolf, hunting capital vessels caught alone. The Wolf is similarly an excellent choice for well-equipped pirates or more larcenous Rogue Traders.
On the issue of balanced designs, I've found that they generally under-perform, so I rarely build vessels this way. I'd love to hear from anyone that prefers such things.