I could just about write a book on this subject right now, but I'll leave that to Muhammad! I just went through the same thing you're going through. In summary, my advice is to get the factory New Holland loader if you can get a decent price on one! You should also be sure and kick yourself once a week for not getting the loader when you bought the tractor, because you're going to pay more now. I bought a Bush Hog M246 and regret it. That being said, the M146 might be OK. There is information on their loaders on their web site,
www.bushhog.com. The Woods 1012 might be OK, but probably too big for a TC18, so consider the 1006, 1008, or 1009. There is a .pdf file on the Woods loaders on their web site,
www.woodsonline.com. The main thing you need to do is to do what I didn't do, and that is to actually see the loader installed on a tractor like yours (same exact model) and then decide if you like it or not. Find out how much the loader itself weighs, how much weight is left on the tractor when the loader is detached, and how much weight you'll need for ballast. Find out if any mounting brackets get in the way of engine maintenance, even when the loader is detached. Find out if any mounting brackets go under the tractor to the drawbar and find out if they get in the way of a mid mount mower (if that matters to you) or reduce your ground clearance.
I think any loader they make these days is detachable from the tractor, but double check that. I can tell you that the Woods 1012 and the Bush Hog M146 are both detachable very easily and it only takes 5-10 minutes. If you get quick attach bucket option, make sure it's the Skid Steer compatible type, or you'll be limited on what attachments will fit it. The quick attach bucket option will add some weight to the front of the loader. I know that the Bush Hog M146 does not come with the quick attach bucket option.
You might want to read these posts:
FEL options for my Boomer
Ordered my Bush Hog M246 FEL
When is rear ballast needed with a FEL?