Fireballs: They all right items. Hitting multiple foes and making them spin out longer than regular bananas, plus disabling the backseat driver from doing stuff gives this a big plus. One disadvantage though, it won't help you if you are 8th, plus you can hit yourself quite easily, due to the unpredicatble nature of fireballs.
Hearts: Good item. Too bad they go away when you get lightning'd and they can't absorb Spiny Shells or Chain Chomps, but that makes the list of what they can't absorb. They can make you pick up special items such as Bowser Shells, though. They are the ultimate defensive item, except when used against fireballs. Too bad they also use up hearts if you pick up a Mushroom, Lightning Bolt or a Star, but that can also be a good thing if you want to use it later
Eggs: They're pretty much meh. Why? Eggs can only go a certain distance before they break, unlike Red Shells, which travel until something hits them. Plus, items fly out in front of the opponent, giving the opponent a chance to drive into a star. They're great when used in first, since a star might pop out, but could also hinder you because a Bob-omb or items other than a Mushroom and a star can fly out and slow you down. The plain old Red Shell is a much better item when it comes offensively.
Triple Red/Green Shells: They're great items, especially Triple Red Shells, which are something CPUs can never obtain for some reason. One thing bad about them is that you lose 2 out of 3 or 1 out of 2 when you get hit. Still, triple red shells actually do something to your opponent if you manage to hit all three of them in your desired spot, and maybe to an extent the triple green shells can too. They're also great defensively, since you get three chances to block items coming at you. They're not as great as they are in other Mario Kart games, but still pretty decent.
Giant Bananas: Giant Bananas only do great offensively when an opponent is trailing behind you or if you're using them in a ramp. Defensively, they're spectacular. The only things they don't block are Chain Chomps and people using Stars. They do deflect Bowser Shells, but split into three when a Bowser Shell hits them. The three bananas left over also serve a just as great wall as the Giant Banana. Giant Bananas are the best defense item in the game, hands down.
Bob-ombs: Bob-ombs can be a great or bad item, depending on how you use them. Once caught in the blast radius, you or your opponent can get tremendously slowed down, and also lose your items and get dragged for a while. Bob-ombs are a hit and miss item, basically. Bob-ombs are great during the beginning of the race, due to congested nature. They're not that great later in the race, but are great for hindering rivals if they are just the right distance.
Chain Chomp: Chain Chomps are the ultimate item for getting back on track in the race. They plow through everything, except people using Stars and Fake Item Boxes. They are awesome offensively, since any opponent that gets caught in the Chain Chomp gets flipped and the back driver starts dragging. They are also very fast and have auto-pilot, meaning you can just sit back and make your Chain Chomp do the work. The Fake Item Box weakness is one thing to be concerned about, though. Also the kart has vulnerability too, so users of the Chain Chomp are susceptible to rear attacks. Chain Chomps are also not that great when they end in a curve, which makes the kart get off course quite easily. Overall though, Chain Chomps are beast.
Bowser Shell: Bowser Shells are pretty similar to Bob-ombs; they are a hit and miss item. They can destroy many stuff, including Giant Bananas, although Giant Bananas deflect them. They are great when thrown backward, where they can devastate the racers in their path. Thrown forward, they make a great or bad item offensively, depending on who and what they hit. Whoever gets hit gets flipped and dragged, a major hindrance for either you or the opponent, or even both.
Golden Mushroom: Golden Mushrooms are usually excellent items, but are pretty bad on places such as Rainbow Road or places with many curves. Golden Mushrooms give about a slightly slower speed than Chain Chomps, but a major advantage of a Golden Mushroom is boosting whenever you like or taking major shortcuts. Golden Mushrooms can make racers lose their items, but that's about it defensively and offensively. Users are pretty much wide open to attack when using the Golden Mushroom, but homing items are usually the only threat to users of the Golden Mushroom, due to the speed of the karts when used.