Aves Apoxie Sculpt - This one's the most common putty recommended by modelers for smooth figure
model work and such. Some say it hardens very hard such as to be difficult to sand once fully cured, though. It's a bit pricier than some of the other options, though.
UPDATE: Aves is the best sculpting two part putty I've used for capturing fine detail, but it's not the strongest. Thin or narrow parts can be a bit too fragile.
Magic Sculpt - Lately I've been using one called "Magic Sculpt by Wesco", which I bought economically on eBay in a small quantity. It's worked very well for me. When mixed well in equal parts, it solidifies very solidly in an hour or two and is reasonably sandable. It's also very strong. I've based my brass rods in it in making my orreries and it holds quite well.
Bondo - Award winning modeler Lou Dalmaso seems to prefer Bondo much of the time in his weekly modeling videos. From scanning the forums, I think most guys buy the small 4.5 oz tube of premixed called "Bondo 907 Glazing and Spot Putty". It's intended for auto body work and may not be great for use on some plastics. Some guys say they prime before using it. Some quotes found: "The best way to apply the Bondo is with toothpicks." "The best way to shape the Bondo is to use small pieces of 220 sandpaper. I find that working with small pieces about 1"x1"."UPDATE: I've used this one part Bondo product several times now. It is a nice hard putty, but can be quite runny out of the tube. It also has a pretty strong odor, so I only use it in the garage.
Hardware store epoxy putty (like Rectorseal EP-200) - Lou Dalmaseo doesn't use these for filler as much as an adhesive in building resin models. He finds regular 2-part epoxy too runny for some use, so he uses this in it's place. For instance, he used this type of putty in attaching starship nacelles because it seems to hold the part pretty firmly in place. He does try to scrape off excess, then sand it later and uses other fillers for final smoothing. In my own use of this type of putty, I found it super hard and strong, but set too fast and was very hard to sand or work once hardened. Perhaps hardness varies by brand.UPDATE: I've had a lot of shelf life problems with this product. You really need to use it fairly soon after opening or at least one part seems to turn hard before you know it.
Squadron Green Putty - Single part putty in a small tube that many modelers like a lot. One guy said
it can be thinned and smoothed with Testor's liquid model glue.
Milliput - This is another 2-part putty some modelers prefer.
Sikkens Kombi Putty - One modeler called this "the best spot putty on the planet". He sometimes uses Evercoat body filler for large areas, then then skims the top with Sikkens. He says he buys the smallest size and you have to get it from an automotive paint jobber that sells Sikkens products. I found a product sold online called Pronto Kombi Spot Putty that may be the same thing, but we'll have to try it out sometime.
Tamiya putty - One modeler says this "buries" Bondo, though he uses both.
UPDATE:
Pratley Steel Putty - I needed as strong a putty as I could find for use on a model car axle and this filled the bill well. It's a two part putty that comes in a fairly small package, but it's the strongest putty I've used.
