If you haven't already, you should visit Harbeth's web site, which is excellent. There is also a user forum, accessible through the web site, which addresses your question in several threads.
The LS 3/5A is designed to the legendary BBC mini monitor spec. The Compact 7, Monitor 30, and Super HL5 is where the decision lies. They sound far more alike than different. Harbeth has a Monitor line, which includes the Monitor 30 and Monitor 40. These uses the Seas Excel Millenium tweeter and are designed to have the kind of extremely flat frequency response demanded for monitoring situations. The Compact 7ES and the Super HL5 use a less-premium tweeter and are purported to have a very slight midrange depression in the frequency curve (what some have called the "BBC dip"), which is considered more to the liking of most home music lovers. The Super HL5 also has a super tweeter, but it's main difference from the Compact 7 is greater cabinet volume and, hence, greater bass extension and output. Of the 4 models you list, the HL5 has the most bass and is physically the largest.
If you can, audition the Monitor 30 against one of the other two. Between the Compact 7 and the HL5, it has been a choice for more or less bass (the HL5 can be too much bass for smaller rooms). However, the Compact 7 has recently been revised (now Compact 7ES-3) and the buzz is very good about it, though I have not heard it. I own the Super HL5 and have only very limited expsore to the other models, though I am considering picking up a pair of Monitor 30s in order to get a better handle on how it differs from what I have. Hope this helps.
The LS 3/5A is designed to the legendary BBC mini monitor spec. The Compact 7, Monitor 30, and Super HL5 is where the decision lies. They sound far more alike than different. Harbeth has a Monitor line, which includes the Monitor 30 and Monitor 40. These uses the Seas Excel Millenium tweeter and are designed to have the kind of extremely flat frequency response demanded for monitoring situations. The Compact 7ES and the Super HL5 use a less-premium tweeter and are purported to have a very slight midrange depression in the frequency curve (what some have called the "BBC dip"), which is considered more to the liking of most home music lovers. The Super HL5 also has a super tweeter, but it's main difference from the Compact 7 is greater cabinet volume and, hence, greater bass extension and output. Of the 4 models you list, the HL5 has the most bass and is physically the largest.
If you can, audition the Monitor 30 against one of the other two. Between the Compact 7 and the HL5, it has been a choice for more or less bass (the HL5 can be too much bass for smaller rooms). However, the Compact 7 has recently been revised (now Compact 7ES-3) and the buzz is very good about it, though I have not heard it. I own the Super HL5 and have only very limited expsore to the other models, though I am considering picking up a pair of Monitor 30s in order to get a better handle on how it differs from what I have. Hope this helps.