Set track is obviously the easiest of track to lay, push it together, connect your controller, and you're ready to run your trains. It's biggest draw backs are that it has too heavy a rail section (it would be 9" high if it were fullsize!), and it doesn't "flow" like prototype track does, it is either straight or curved.
With
code 100 flexitrack you can lay it to look more like the prototype, with that almost fluid like sweep as a straight gradually becomes a curve, and even long sweeping curves rather than straights. It still has the heavy rail section of set track though, and you will need to cut the rail and fit your own fishplates (rail joiners).
The only differance between code 100 flexitrack and
code 75 flexitrack is that code 75 uses a scale rail section, so it look alot better, and you can still run any ready to run models on it.
However most 00 track (Peco, Hornby, etc.) is actually built to H0 scale and is designed for the American market, this means the sleepers are too small and too close together, therefore some people use track from C&L or SMP which has the correct sleeper size and spacing for British 00 models.
The only problem here is that you need to scratchbuild your points (it's actually alot easier than it sounds!) using parts available from C&L, or have them professionally built for you by firms such as Marcway.
You can still run most ready to run models on
00 finescale trackwork, but you may need to replace the wheels on some older models (say anything older than about 10-15 years).
Next problem is that 00 track is actually too narrow for the loco's and stock (2.33mm or a scale 7 inches) so if you want to correct this you have 2 options.
EM (short for Eighteen Millimetre) uses a gauge of 18.2mm, like 00 finescale there is flexitrack available from SMP and C&L, and you will also have to scratchbuild your points using parts available from C&L, or have them professionally built for you by firms such as Marcway. You will also have to change the wheels in all your loco's and rollingstock to suit the new gauge, which can be quite difficult in EM.
P4 (short for ProtoFour) uses the exact scale gauge of 18.83mm, there is also flexitrack available from SMP and C&L, and point kits are available from Exactoscale (these are about easier to build than plastic wagon kits), or you can scratchbuild just as with 00 finscale and EM (I have a single slip taking shape on my work bench at the moment), or even have them made for you by firms such as Model Signal Engineering. You will also need to cahnge all your wheels to suit the wider gauge, but it is often easier to do this in P4 than EM.
If you'd like more info on P4, take a look at my site -
P4 Made Easy - shameless plug I know
Also here is a length of Peco 00 code 75 flexitrack beside a length of C&L P4 flexitrack for comparison. Note on the P4 track the longer, wider sleepers are spaced further apart, and the gauge is considerably wider, which is correct for 00 scale models.