I am going to break the weapons into two general categories: short-medium range and medium-long range. Most of the maps in Call of Duty 5 tend to fall into one of the two categories as well (regarding combat ranges). For example, Asylum is a short-medium range map while Seelow is almost exclusively medium-long range.
Typically, fully automatic fires over semi-automatic weapons. In small, close quarters maps, there will be a lot of movement and running around. Submachine guns have exceptional mobility, a great rate of fire (ROF), great damage, decent penetration, and decent range. Shotguns could be used, but only in very small, bound maps such as Dome or Asylum, but let's face it, outside of 10 feet in front of you, you're screwed. However, an SMG would still yield greater benefits in the same scenarios with their greater range, higher ROF, ammo, etc.
Thompson – Great damage and above average penetration. Get used to the iron sights and use the drum magazine for more magazine capacity (less reading).
MP40 – Higher minimum damage than all other SMGs (29 min damage). Lower penetration than the Thompson, but on par with the rest of the SMGs. Moderate recoil, follow up shots can be difficult, iron sights can be difficult at longer ranges. My suggestion is to use the iron sights with the drum magazine.
Type 100 – Higher magazine capacity than the Thompson (30 rounds), but less penetration. I personally do not use the Type 100, but it is a viable option. The same suggestions for the Thompson goes for the Type 100 as well.
PPSh – Low damage, but a stupidly high rate of fire. Definitely use a drum magazine since you will need more hits to kill a person. The extra ammo will also come in handy when engaging multiple targets or clearing out rooms. I prefer this weapon in small maps because I like the high rate of fire (ROF). This can cause a favorable pshycological response from your opponent. Imagine you're running around, then hear a PPSh go off. Suddenly your screen is read and each time you get hit your screen twitches. It's very hectic and difficult to engage someone who has you engaged like that. Steady aim shines with this gun and it will help you clear rooms faster, run and gun, jump shoot, etc.
I strongly urge you to get comfortable with a rifle of your choice, whether it be bolt action or not. You will need to long range capabilities and damage of a rifle when playing in larger maps. I'm not going to mention the bolt-action rifles because their characteristics (damage, range, ROF, etc) are similar between them all and it should be up to the player to decide which weapon he likes the best.
M1 Garand – Has the highest damage in the rifle category. Usually scores one hit kills without a scope (but with stopping power), however; linking in the middle of a clip takes longer than usual. Add a scope for more damage, or use iron sights for quick shots. Downsides to this weapon are the recoil (think M14 recoil in COD4), magazine capacity, and referring time. The iron sights are exceptional, only second to the iron sights on the bolt action rifles.
M1A1 Carbine – Same damage as the SVT-40 and Gewehr-43, but with a larger, 15 round magazine. The recoil is minimal, about on par with the Gewehr-43's recoil (or the G3 in COD4). I like this gun because of the minimal recoil which allows me to quickly turn and get a few shots off without having to wory about my follow up shots. It's reliably easy to aim while you're shooting with this gun. Also, the damage is great; with stopping power, about half of my kills are one hit kills and the other half take two hits. The iron sights are very good and it's not hard to get a clear picture from long range. The only gripe I have is the thickness of the rear sight, which obstructs your view when aiming. My suggestion would be to use the drum magazine and get comfy with the iron sights. The more ammo you have, the less you have to worry about relating, engaging multiple targets, getting killed while referring, etc.
FG-42 – Out of all the machine guns, the FG42 shines above the rest. While doing the least amount of damage out of all the machine guns, the high rate of fire, accuracy, mobility, and time to reload makes up for it. One quick burst of 2-4 rounds will kill somebody provided that they hit. The recoil on the FG-42 is very controllable unlike other machine guns such as the BAR. You'll hardly notice your aim sway while you shoot. Mobility is not hampered as much versus the heavy machine guns either, which means that you can sprint faster for longer distances. One downside is the 20 round magazine capacity, however, communicating takes substantially less time than it does with heavy machine guns such as the Browning 1919. The iron sights on the FG-42 are exceptional and it gives you a clear view of your target. The front sight comes to a point, which makes long range aiming and shooting more accurate. I do not like the telescopic sights because they sway too much, so I opted for the iron sights.
Again, everyone has different tastes and the only way to find out what weapon suits you is to play the game! Find a weapon you're comfortable with and stick with it. I chose to list the more common and preferred weapons, but there's no reason to say that you will not own with a weapon that was not listed.