Some of the good ones are 'interchangable' with many others, I would try for those. That way you can start with the basics and it will be easy for friends/family to add to it over time.
We started our son with the Ikea set (9.99 for track and trains) because they are 'standard' and work with all of the standard sized Thomas tracks/trains/accessories.
We also have an imaginarium set and it's great. Little dude can use the Thomas trains on it and we don't have to pay for those super expensive tracks. It's held up pretty well so far too.
If you're going to start a collection I recommend the Take and Plays (Thomas the Train). They are relatively inexpensive (this is a big factor when you start buying 50 different trains) and my DS loves to put the tracks together on his own. They work well on all surfaces. We have all the different kinds (Trackmaster, Wooden, and Take and Play) and I recommend the Take and Plays the most because of cost + interest. Good luck!
Re: best toy train set?
Some of the good ones are 'interchangable' with many others, I would try for those. That way you can start with the basics and it will be easy for friends/family to add to it over time.
We started our son with the Ikea set (9.99 for track and trains) because they are 'standard' and work with all of the standard sized Thomas tracks/trains/accessories.
I bought this one for DS. It is interchangable with the Thomas trains.
https://www.toysrus.com/buy/vehicles-hobby-r-c/trains/train-tables-playboards/imaginarium-city-central-train-table-5f5e9b1-11766021
We started with the Circo brand from target. It is wooden and the pieces are interchangeable with all the standard wooden tracks.
We got him this set from Amazon for Christmas when it was on Lightning Deal for $39.99.