I've got a Mosin nagant, SVT 40, and SKS.
SKS is definitely the better option in terms of practicality, easy to clean, cheap ammo, cheap gun, aftermarket parts, loads of trouble shooting info available.
The SVT 40 is a nice bit of rifle if you ask me, especially with the lever arms sale making it nearly price competitive with an SKS. But the rifle itself feels like a solid platform, and the detachable mag is a definite bonus.
I imagine there would be a lot more after market parts if they weren't 1200ish dollars down in the states.
Also as far as nice features goes the SVT 40 beats out the SKS in my opinion, no such thing as a slam fire in a SVT really, as they have that internal spring, then you also can take out your cleaning rod with a button rather than screwing it, minor though that may be I think that's cool.
The SVT just feels more mechanically thought out, whereas the SKS seems like it was manufactured for just bare bones reliability and mass manufacture, which isn't bad mind you.
And yea, SVT+Mosin= fun fun fun all with the same cartridge.
In the end though you'll probably have more fun with another SKS to tacticool all to crap, I'm thinking of buying a Chinese one for that express purpose.