100% for fun - you can't beat a Ruger .22/.22M SA revolver with a long barrel. Cheap, accurate and safe. Ammo is the cheapest thing that isn't a pellet. Wear a cowboy hat and quote spaghetti westerns between shots. Wallow in the savings of having bought a used one for $150.
I am not a fan of the 9mm for defense or plinking. Its fast and accurate but it does not hit hard and is not cheap enough compared to better rounds to make up for it in my wallet at the range. The .40 S&W was designed as a law enforcement round because of the suckitude of 9mm and is relatively new (the early '90s). It has nearly identical accuracy (drift/drop) to the 9mm but significantly more "stopping power" in the high energy loads. Tons less recoil than a 10mm or 45ACP so can be used in smaller frames. Cheaper than .45, a little harder to find but Walmart has them around here.
I despise Glocks. I don't have a tangible reason but IMO they feel, shoot and look like a Chinese knock-off of a better pistol. They are effective and a lot of good shooters swear by them but... a lot of good shooters also have fwd automatic cars. ;) Since I mostly shoot for fun I want a weapon that does more than just get the job done.
For lefties who carry - SIG and H&K both make excellent frames that are swappable.
I have an H&K USP in .40 S&W. It is a great all-around piece. It is light, extremely well balanced, accurate, never jams on E36 M3 ammo and can be carried cocked -n- locked so even if you drop it in full "ready to rock" mode - it wont shoot you in the face. It is also super easy to strip, clean and reassemble. The price was a bit high but not out of proportion to what a top end "off the shelf" of any ilk goes for. The one area it lacks is that it is barely small enough to carry unless its winter. I rarely ever do except to tuck it out of sight while going to a restaurant or something so its not in my car - and it can be done but if you live where you are in shorts all year it won't be comfortable AND concealed at the same time.