I also recently went down the first rail camera road. I wanted good $ value, good parts and accessory availability, precise construction, high reliability, and stability--all combined in a relatively light weight camera. Arca Swiss, Toyo-View, and a few others have most of this, but aren't readily available on the used market for what I could afford. So the search quickly boiled down to a choice between one of the Horseman L frames and a Sinar F series. Being an ex-engineering/technical type, either was attractive. To be honest, at first I actually liked the mechanical design of the L-frames better, and prices in the used market were comparable. However, I finally bought a nice Sinar F2 kit because:
1. Weight. At about 9 lb in the basic configuration, the F2 is several pounds lighter than the Horseman L's, and my intended use was 100% as a field monorail. Not backpacked, just carried in my 4WD truck and wheeled/lugged to the site.
2. Availability of accessories: Although many things will interchange between the two, the used market is practically flooded with used Sinar accessories, usually at very attractive prices. Horseman also put out a lot of accessories, but search on ebay for Sinar vs Horseman and you'll see what I mean about availability of parts and pieces on the used market.
3. What the others use: Although many do own and use L-frames, a zillion LF
photographers far more experienced than I cut their teeth on (and still use) a Sinar F or P series (the P series got ruled out for me because of weight). That means when I screw up or have questions, I can call on a huge base of "technical support" out there for help.
Now that I'm learning to use the F2, I'm really starting to like the tilt/focus aids and DOF calculator built into the controls on the standards. So although I still believe the larger/heavier Horsemans are great cameras, I believe in the long run I'll be happier I went with Sinar. In a wheeled Pelican soft case with half a dozen film holders, two lenses, rail extension, and all accessories (even a bino hood thrown in) the whole rig is still only 28 pounds, and is very fast and easy to set up.
Good luck in any case!