Would a vampire get more energy, warmth or nutrients from fresh blood as opposed to frozen? What about fresh blood vs. old blood?
Nutritionally speaking, freezing food does little to destroy nutrients, but there are some issues If you are serious about this, there is a paywalled article, Preparation and Usefulness of Frozen Blood. One point that may interest you is that frozen blood is stored at very cold temperatures, lower than -65 C to prevent essentially all damage (other than the freeze/thaw cycle itself)
Commercially frozen food is often blanched prior to freezing, which does result in some nutrition loss in terms of vitamins C and B1. But the bulk nutrients (fat, protein, carbs) and minerals are unaffected or nearly so. Commercially speaking, frozen food may be more nutritious than fresh food as the fresh food is often harvested early to make it possible to arrive on your plate apparently fresh after the delays associated with shipping whereas frozen food can be harvested at peak freshness then frozen quickly.
Freezing blood would possibly affect the taste, and the freezing process would certainly damage some of the blood cells, but considering that frozen red blood cells are used in transfusions cells with an 85%-95% survival rate of that process the red blood cells should certainly be OK in bulk if they receive a suitable cryo-preservative treatment - mostly glycerol. Frozen blood cells are prepared by centrifuges to remove plasma prior to freezing and must be washed free of the cryo-preservative after thawing. It is entirely likely that vampires would not need such special methods to preserve cells as the food need not necessarily still be living cells to be nutritious. The damaged blood cells might actually be slightly better in that breaking down of cells walls, etc. in the process may make the food absorbed more easily.
Note that frozen whole blood has been done of course. Paywall Freezing of Whole Blood article from 1949 shows that this is not a new thing. Medical use of blood presumably has different valuable aspects to consider than use as food.
Some foods are more obviously damaged in freeze/thaw cycle than others - never actually tried blood of course, but I know that frozen strawberries do not have the same texture as fresh strawberries. Blood is not a homogeneous fluid. The freezing and thawing process will result in some separation of components, and some degradation of texture. Due to component separation, etc. I would expect frozen blood simply to be less desirable than fresh even if it is nutritionally similar. It might still be useful because freezing can preserve food for years and an emergency reserve might be worth having. Of course, to drink the frozen blood, you would need to thaw it before serving.
Refrigerating most foods has very little of the nutritional, taste, and texture loss association with freezing them. If storage is short term (usually up to about 1 month), simple refrigeration is almost always preferable to freezing. I can totally imagine that some vampires would develop a taste for chilled blood, just as some people enjoy iced coffee, tea, etc. There is considerable literature on the topic of blood refrigeration, but the taste aspect is not studied.
Even more desirable in some cases is simply to irradiate the food with UV to kill off germs, etc. and seal the food until it is needed, e.g., milk in a box stored at room temperature seems to be a good analogue and is common in some countries. Given vampire's reaction to sunlight, UV sterilization may not go over well.
Freeze dried blood, or blood jerky have not been investigated to my knowledge. Likewise removal of blood plasma to make a more concentrated food source may also be useful. aka, blood ready to eat emergency rations.
Also note the some vampires do not kill their prey at all, preferring (or perhaps requiring) fresh living blood. Presumably your vampires do not have this requirement.
The temperature of the blood doesn't directly affect its chemical energy content but does have an energy cost to start to use it because it will cool the vampire down, requiring the expenditure of energy to warm itself back up. I believe it would be better to not consume frozen blood, though if frozen blood were thawed first it probably would not have any negative effects.
As far as the age of the blood, it would depend on how it gets its energy from the blood. If chemicals in old blood break down causing them to not be as nurishing, then old blood would be an issue. You may also have bacterial/viral issues as the blood grows bad stuff. All this really depends on the metabolism of the vampire.
An entertaining possibility has nothing to do with nutrition as such. Let's say that a vampire's energy requirements are supplied by all the components of plasma, as well as the structural proteins in red blood cells. Hemoglobin, however, also has euphoric effects as well as nutritional, and makes the vampire feel, well, very good indeed. This hemoglobin-induced psychological effect has evolved because it makes it easier to maintain feeding behavior on the humans which surround him, and which otherwise might engage his sympathies. After all, if vampires are a human subspecies they presumably maintain much of the social nature of the parent stock.
In this case, frozen and thawed blood would have a more immediate effect than normal, since the ruptured red cells would not need to be metabolized to release hemoglobin, and the result would be an enhanced, briefer rush. Sort of like the difference between cocaine and crack.