Well, it's been a while since I've used Gosen Polylon, and I still have a half a reel left of it. Now using a lot of TiMo Luxilon.
First off, although both strings are referred to as "poly" strings, they are made of very different stuff. Polylon is made of polyester, which is what used to be the only plastic referred to as a "poly". Luxilon TiMO is made up mainly of Polyether (or zyex, or Polyether ether ketone, or PEEK), which is a much different material, as well as some other material (presumably Ti and MO to give it more wear resistance - I'm just guessing here - TiMO wears better than the regular Big Banger).
Polyether is a much tougher and more elastic plastic than polyester. It is known for not losing its elasticity and is also used as a synthetic replacement string for gut strings in musical instruments (just like tennis racquets!).
Both Polylon and TiMO have excellent wear resistance, especially when used with a softer nylon cross-string in a hybrid. Both are relatively stiff strings and will feel very stiff at higher tensions.
Polylon has this very brief (maybe 1-2 hours or less of use) period of time after stringing where it actually feels somewhat elastic and powerful. After that, it goes dead, Dead, DEAD. Very little power after that.
TiMo retains its elasticity and power for a much longer period of time. It resembles gut strings in this respect, although it is not as forgiving or as powerful as a top quality gut string.
Stringing the two strings is also different. Polylon is much stiffer, and feels almost like stringing aluminum wire. Make a bend in Polylon, and the bend stays in the string forever. Polyester is a more brittle material as well, and so you have to be careful not to keep bending any part of the Polylon string too much or it will crack and break.
Polylon, is of course, dirt cheap whereas TiMO is priced at premium synthetic string levels.
So, bottom line is that if durability and price are the only considerations, then Polylon wins hands down. If you rather play with something that has a crisper feel and decent power AND also has great durability, TiMO is not hugely more expensive, and so is well worth it.