I think I just crapped my pants after seeing that movie. Ok, some thoughts and opinions. Here's the dealio. I am going to make a little list with pictures showing all possible/feasible ships that could be used.
UNSC CAPITAL SHIPS:
1. UNSC Super Carrier. A 1.5km long Carrier deemed big enough to be called a capital ship. I would advise ignoring the super carrier, although it is a ship, they were hardly any, and to implement something like that is just weird.
Armaments: Archer Missiles. One normal Magnetic Accelerator Cannon. Carries multiple groups of Long and Shortsword Fighters/bombers.
Examples: Stalingrad
2. Marathon Class. 1.2 km long. The most reliable and most used capital ship of all. Similar to a battleship.
Armaments: 3 Heavy Magnetic Accelerator Cannons. Oversized Archer Missile pods. Many 50mm point defense (possibly anti-fighter or for taking out smaller targets). Multiple Shiva Nuclear Devices.
Examples: UNSC Leviathan.

3. Halycon Cruiser Class. 1.1 km long. Obsolete cruiser, replaced by the Marathon. The ones not scrapped are being outfitted with better armor and weapons. Not as popular/reliable and less used as the Marathon's.
Armaments: (Keep in mind these are the new weapon outfits, older ones were much less). 1 Heavy Magnetic Accelerator Cannon. 4 Shiva Nuclear Devices. Over 100 Archer Missile Pods. 40 50mm point defense guns. Also multiple compliments of longsword fighters.
Examples: Pillar of Autumn.

UNSC Frigates:
1. UNSC Destroyer. 485 meters (7 meters long than a regular frigate). Very similar to a frigate, but twice the armor. Many were produced, very efficient and were used to accompany Marathon Cruisers.
Armaments: 2 Normal Magnetic Accelerator Cannons. 3 Shiva Nuclear Devices. 26 Oversized Archer Missile Pods. 8 50mm point defense guns.
Examples: Glasgow Kiss
2. UNSC Frigate. 478 Meters long. Most built ship in the UNSC arsenal. Extremely reliable ship. Well rounded for multiple uses, including space combat and ground assaults.
Armaments: 1 regular Magnetic Accelerator Cannon. 1 Shiva Nuclear Device. 30 Archer missile pods. 8 Point defense guns. Multiple Longsword fighters.
Examples: Aegis Fate; Forward Unto Dawn.

3. UNSC Prowler. 162 Meters long. The most used type of stealth ship. Can easily be invisible as long as used low engine power and compromising speed. Mainly used to gather intelligence and observe.
Armaments: 14 Hornet Mines. 2 or more Pulse Lasers.
Examples: Point of No Return; Dusk
UNSC Misc ships:
1. Phoenix Class Colony Ship. Longer than 1500 meters. Primary UNSC ship used to colonize uncolonized planets. Very large ship.
Armaments: 1 regular Magnetic Accelerator Cannon. Multiple Archer Missile pods. Multiple 50mm point defense guns. 1 Shiva Nuclear Device.
Examples: Spirit of Fire.

2. UNSC Mobile Repair Station.(AKA Cradle). Length Unknown. (BIG). A refit and repair station that was capable of traveling System to System. Was used to block a covenant volley in the Battle of Sigma Octanus IV.
Armaments: Unknown. Most likely none.
Examples: Cradle
And theres the UNSC categories. Keep in mind I left out multiple ships that I deemed useless/hard to fit into the SINS unique gameplay. My opinion on how the UNSC ships should work. The normal attack is a MAC cannon fired every 5-10 seconds depending on ship. One of the special abilities is a Archer Missile volley which has a low antimatter and recharge time. Another special ability would be the use of a Shiva Nuclear weapon, which would have a very high antimatter and recharge time. The 50mm guns would always be active, attacking fighters, but would be very weak. Possibly another special ability is a quick volley of MAC shells using average antimatter and recharge time.
I also think that the cruiser category should be tossed out, and just stick with frigates. I also, really think that we need to toss out all ideas of any type of UNSC ships having shields (come on guys, I mean really). And we really need to keep things less complicated and keep stuff simple.
Now onto the Covenant.
Covenant Capital ships:
1. CCS Battlecruiser. 1700 meters long. The most common capital ship employed in their navy. Very well known, and very strong.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers.

2. Reverence Class Cruiser. 3000 meters long. Extremely powerful capital ship, not widely used.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers.
3. Covenant Battleship. 2000 meters long. Almost as commonly used as the CCS class. Very well known also.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers.
4. Covenant Carrier. 1455 meters long. Large Carrier, employs hundreds of Seraph fighters. Not very common. Also used to direct smaller ships.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers. Also contains over 100 Seraph fighters.
Covenant Frigates/Smaller class ships:
1. Covenant Frigate. 1000 meters long. The most common ship in the Covenant arsenal. Very well known ships and used as cannon fodder.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers.

2. Covenant Cruiser. 1000-1200 meters long. Usually paired with a CCS class, these ships are bigger than a frigate. Not as widely known.
Armaments: Standard fitting of Multiple Plasma Torpedo launchers and Multiple Pulse Lasers. Possible Seraph fighters on board.
3. Stealth Corvette. Less than 485 meters. Ships built in very small numbers. Very small, similar to a prowler.
Armaments: Unknown. Minimal.
4. Agricultural Support Ship (could be used as colonizer). Unknown length, most likely small. Used to feed elites and prophets.
Armaments: None.

Well there it is. Now heres my ideas on covenant weapons. Basically, every ship shoots plasma torpedoes every 5-10 seconds in barrages. A regular special ability with small cooldown and small antimatter usage is point lasers. Also possible fast barrage special ability for plasma torpedoes. Now, I also think that all the other covenant ship classes that some of you know should be tossed out. Since almost none of them have any known pictures, its impossible to do anything with them. And to end the debates, make the Covenant have powerful shields but sucky armor. Also, make their planet to planet jumps faster. Alright, well that's all I have to offer. I might make another one of these but with buildings and space stations. Enjoy. Also somebody should stick this at the top of the thread or w/e but its up to you. Also you guys probably already figured this out, but any ship without a pic doesn't have one. And here's a little chart showing scale.