The tiled look is the enemy of all good texturing and you will always get that when using the "Fill" method. Can't comment on the HOG method, I don't know how to do it and I've not seen any results, but it does sound rather clever.
The copy-and-paste method that nicky9499 referred to is the one I use for laying down base textures. It combines complexity and variation which you can control, plus mindless convenience for doing large areas. Some things to keep in mind;
- Do detailed manual texturing on one or two boards only until you get something that looks typical of what you want. Swirl/rotate textures and vary the scale to impart greater randomness as you go (some say this results in a frame rate hit, but I think it's minor).
- Copy/paste sections (and maybe even different sections) of those boards to the rest of the layout. You can copy quite large areas likes this, even bigger than 1 board, but pasting with smaller areas allows manual variation on a finer scale.
- Having the mini-map open and zoomed out is a good way of seeing where you're at while you're doing this.
- Vary the direction of pasting (using the little copy/paste tool compass) to get even more randomness.
Having laid down your base texturing, you might want to add second-level detail by highlighting hilltops and ridges with lighter textures and valley bottoms, gullies, rivers etc. with darker textures. Unfortunately this is manual, but I guess you could just choose to do it in areas that will be visible from the train.
Third-level detail would be features like road and track beds, rockfaces, cuttings, shadows under bridges etc. Again, it's manual but the visual payoff is large and it's fun if you're artistic!
[another suggestion: To keep track of all the (custom) textures used and to locate them quickly in Surveyor, analyse the layout with Trainzobjectz then use it to re-assign them to a common "region" (something starting with A, such as "Active"). They will then be displayed as a group at the top of the list on the Surveyor pallet.]
Dean