Well it depends on what your budget is, where you intend to stop, and perhaps even what type of vinyl you like to play.
I have owned TD 125 in the past, and own a TD 124....along with a couple of other tables. Now there are people who will disagree with me, but the TD 124 is the high water mark for Thorens, at least for the tables that were widely distributed. But that arm is a bit of a relic, and you can achieve far better performance with more of a current production piece. But even on the used market, a tone arm can cost at least $250 to $300 for a more "modern" older piece. Now if you have the appropriate head shell for that arm you could at least get a couple of hundred for it. If it does not have the head shell it is darn near worthless, as on Ebay the head shell sells for $100+...actually closer to $200. Now there may be some vintage cartridges that will work well in it, but I am not real well versed on that info...someone else will have to give it to you.
Now I don't care for the 125 as much as I do the 124, but it is still a darn nice table. And that price is very reasonable for the tone arm and table. That arm will normally sell in the $350 to $400 range, and perhaps a bit more if all the bits and package come with it. With that said, I am not all that fond of that arm either, but it does have its fans. But it is a good solid table, and will give you excellent performance.
One more thing on the 124, and perhaps the 125. If these tables have not had some maintenance done to them you are going to have to put a bit of cash into them. With the 124 you want to lubricate all the moving joints for the controls, idler wheel, and what not. You will probably want to oil the motor, and consider having it refurbished to ensure its longevity. Also the rubber motor mounts should be replaced, and perhaps the plinth suspension mushrooms. Clean the spindle housing out, put new oil in, make sure the bottom plate is not deformed. Oh and replace the belt, and make sure the idler wheel does not have any flat spots. One very important thing to do is make sure the top aluminum plate is flat and true. These are very expensive to replace, and hard to find. Over the years careless people have damaged a number of them, and its getting harder to find replacements. These pieces can sell for the $300 range on Ebay all day long....when you find them. There are a lot of affordable parts on Ebay for the general maintenance of this table.
Good luck with your choice, both are wonderful tables. Give us a bit more info on what you want to do, where you see yourself going, and what you might budget for all of this.
I will leave you with this image. here is a TD 124 built by AK bob06. This is where you could end up one day!
Regards
Mister Pig
