You could do either. There are lots of needy rescues out there, but depending on where you are, the process can be slow to get them, so if you are considering a rescue it would be a good idea to get your applications in to the breed rescues and so forth. For example even though I'm the only official cavalier rescue in Ireland north or south (outside the breed clubs, which don't do rescue in any structured way here) and the breed is one of the most common in the country, it can be months before the right dog comes in for an applicant.
At Holly's age she will likely be happy with any age of companion as long as she has met lots of different dogs and enjoys other dogs' company. Read up on the potential challenges of a rescue -- it is not like getting a dog that has been living happily in someone's home, most of the time. They sometimes have training or behaviour issues and will need a little time and flexibility on the part of their new owners to settle in. Some have never known any kindness at all, or have spent their life so far in a cage. Others might have been people's dogs but mostly, ignored. And some are just happy dogs needing rehomning due to family circumstances. Only very rarely are puppies in rescue so usually, you are dealing with the unknown quantity of an older dog.
That said, almost all settle very quickly. They can also be the most rewarding of all dogs to own -- often they bond far more closely to their owners and are the most loving of dogs. Few experiences match watching a rescue come out of its shell and learn to play with toys, never having had toys, or relax on a bed, having lived in a cage with barely enough room to turn around, or out in a cold garden, shed, or kennel run. Oldies can be extremely rewarding, and many say these are the dogs that grow on them most, because of their sweetness and dignity and devotion. The knowledge that a dog that spent a week in a pound and had reached its last day -- then found a new home and lease on life with you -- is also very rewarding.
I have a lot of links about taking on rescues and what can be expected, stickied at the top of the breed rescue section. People need to be realistic in weighing up whether this is the right choice for them. Some people like the idea that they are rescuing a needy dog, but forget that the dog is -- yes -- often very needy. So I always like to make sure people are ready for the little issues that might crop up, and know about the likely NORMAL things that happen when a dog finds itself in a totally strange environment (no matter how pleasant!). Usually people will get a few days of unwanted behaviour before the new dog beings to settle. On the other hand, people tend to forget that a rescue probably settles in far more easily and quickly than a puppy -- which is likely to whimper and whine when left alone, especially the first few nights, and brings many months of housetraining etc along with it -- there's plenty of work with a pup (more, in my experience, than with any rescue I've rehomed!).
Also: a good rescue will want to match the right dog to the right person and provide full backup. So this lessens the chances of any real difficulties.