The train sets pretty much all fit each other, you can't go wrong!
Our train set grew and grew, it had bits from Brio, Big Jigs, Tesco, Ikea and probably more I forgot.
They all fitted together perfectly except the IKEA which you had to wedge in a bit, typical IKEA
although this was years ago and I think they fit fine these days.
I can't recommend a train set highly enough! It was, hands down, our most played with toy. And not just by the DC, but definitely a firm favourite also with visiting adults, they would actually get down and play with the DC with the trains, which the DC loved. That didn't happen with any other toys except maybe Lego every now and then.
And if the DC do play with it then it's a great toy for Christmas as you can ask relatives etc to get extra bits for it and there's something for every budget.
Also, people reading this thread, please don't forget that girls like trains too! DD got just as much play out of our train set as DS!