Novatron: We used to (fifteen years ago) call Novatrons "Novabombs" because of the high # of incidents of people getting shocked by them, of having connectors arc when unplugging heads, even after turning off the unit and hitting the test button a couple of times, and of having heads meltdown when used in softboxes. They have always been among the most efficient of units in terms of light output. Because of my history with them, they are part of the reason I always use radio slaves to trigger big high voltage flash units. Obviously they have improved because they are still in business.
Speedotron: Speedotron is the workhorse of the American photographic industry. Rugged, reasonably priced, versatile,fast recycling, easy to find as rental gear, and did I mention heavy? The newer units the 1205 and the 2405 are much lighter than their bigger studio brothers, but still heavy compared to the competition. The bigger, older designs are evidently built to US military specs so things like capacitors and diodes are easy to find. Very reliable units. Because they are a 900V unit some fashion photographers, mostly in the Chicago area, use modified Profoto PF heads (better light quality, color temp, and UV coating technology on the flash tubes, and reflectors.)
Balcar is also great, but in my experience and by reputation, can be tempermental and fragile. They make a loud pop when they fire. As strobe makers Balcar makes great accessories, and modifiers.
Elinchrom is better and more reasonably priced, especially for monoblocs. I wish the EL monoblocs had infrared remote contol and that the EL 1000 units had user replacable flashtubes. I don't have any direct experience with the classic studio series.
Comet, in my mind, has always been way overpriced. I have never had a good experience with the PMT battery units, but these have been rental units, not new ones.
Dynalite is a very good workhorse alternative to the size of Speedotron and the cost of Comets and Elinchrom. The M2000 pack used to be problematic but that may now be solved.
I don't like the Paul Buff units but this opinion is based on what I feel is his deceptive advertising. He does have a great reputation for service, and the price is good.
My favorite flash equipment is made by Profoto from Sweden. Great light, great ergonomics, bi voltage (auto voltage tracking withthe Pro 5, Pro 6 and Pro 7 variations), and short flash duration. The Acute 1200 and 2400 units are great: only slightly more expensive than dynalite, many NYC pros have switched to Acutes according to Steve Pollitt at Strobesmith (http://strobesmith.com).
Broncolor. Well that is something to think about after you win the lottery or marry an oil heiress.