I'll add a few minor comments to what
Carguychris said.
Most of everything he wrote was correct. But before someone gets the wrong impression, the 39-series guns were the more reliable guns until the 2nd Generation Model 59-series came out. Early 39-series guns ("Model 39" or no model number stamped on the gun) used a smaller safety lever on the slide and a larger, longer extractor. The extractor was prone to breakage and excessive wear if forced to ride over a case when the slide closed (i.e. manually inserting into the chamber, then drop the slide). These early 39's also had a less than optimal feed ramp.
From the introduction of the Model 39-2 in 1971, the gun's reliability was vastly improved. The -2 featured a new short extractor, longer tang at the rear, redesigned curved backstrap, a guide rod hole in the barrel bushing, improved rear sights and other minor changes including an improved feed ramp integrated to the barrel.
I purchased a 39-2 in 1972 and over the years it fed FMJ, RNL, JHP, JSP and even jacketed and lead
semi-wadcutter bullets without ever jamming. It took about 842 rounds to foul it enough to require tapping the slide to seat it. At 894 rounds it finally insisted on a bath.
I have a preference for the 39-series guns because of their reliability and because I found the 59-series straight backstraps uncomfortable to fire. If you can find a Model 39-2 or 439 for $400 or less, it's a bargain. The later 39xx series guns are worth a little more yet are often seen at low prices too.
S&W Model 39-2 quartet, Mfr dates from 1972 to 1982
The 39-2 is easily carried though it is neither super light nor "compact". It's as easy to carry as a 1911 Commander sized pistol. For all day carry, I use a 3rd Generation Model 3914NL -- essentially a black
Ladysmith. Standard Model 3914's have a straight lower dust cover instead of the tapered one seen below. This one was issued to a police woman who traded it in for a Block...er...Glock 26. Carried a lot, shot little. After cleaning out about 8 years of gunk under the grips the action is smoother and lighter. Using 124gr Gold Dot +P it prints dead on POA at 15 yards.
S&W Model 3914NL, 9mm, 8+1, night sights