There are a lot of similarities, and some differences.
Most synthetic lines are Dyneema SK75 12 strand line. Some are other fibers, but the Dyneema SK75 is probably by far the most common line you will see.
Many of the synthetic lines sold in the US are Amsteel Blue, which is Samson's Dyneema SK75 line.
I've repaired some off shore lines that are reported to be Dyneema SK75 lines and with a handful of pulls or less the lines are in worse shape than my Samson Amsteel Blue line that has a ton of pulls and except for me not putting an abrasion guard in the right spot once my line would look even better.
You do have accessories to look at too. Some of the offshore, budget lines that I've repaired have thimbles, hooks, drum attachments, and abrasion guards that are pitiful. I even have some pieces hanging up at my splicing table that I photographed and have been meaning to do a write up on.
Look for heavy duty parts, the hook especially. The last thing you want breaking is your hook (or other attachment point).
When trying to compare apples to apples, look at line length. Some advertize an 80' line, where others advertize an 85' line. Some measure their line length before the splice, so an advertized 80' line will measure when completed closer to 77' to 78'. Southeast Overland's 85' lines are made with 88' of line. So at a couple bucks per foot 8' less of line can make a significant price difference.
Thimbles also are different and sometimes hard to tell from ads. Southeast Overland uses heavy duty stainless steel thimbles, or even tougher powder coated captive tube thimbles. Some of the 'budget' lines I've seen use tin foil for thimbles. I have one in the shop that crumpled with two light pulls. The thimble is key to keep an appropriate minimum bend radius in the end of your line.
As far as hooks, these tend to be pretty good on synthetic lines except for some of the budget, over seas lines. We use Excel hooks. The last thing you want to break is a hook. Imagine someone smacking you with a piece of rope. Now imagine someone smacking you with a piece of rope with a hunk of steel on the end. You go from hurt to broken or possibly dead.
There is not a huge difference in how lines attach to the winch drum. Taping the line is a decent method since the tape will tear before the line deforms the drum if it is spliced to the drum or bolted improperly. I crimp copper spade connectors also and bolt those to the drum with the small bolt that comes on winches for attaching lines. Some glue the drum connector also to the line but I don't. I want the line to pull free before it damages the drum.
A 12' drum wrap on the winch end helps protect the line from abrasion on the drum and adds some heat protection too. Some less expensive lines don't have this.
You also need an abrasion guard. We offer 10' tubular guards (and we can put any length on the line you want) or 3' heavier duty removable guards - your choice. Some lines only offer 5' guards. A 5' guard is often enough, but I've had times when it is not.
Don't forget free stickers!
If anyone wants a synthetic winch line then give us a call at 864-280-4238 or email Sales@SoutheastOverland.com. We are happy to talk you through the entire process and all your options. We stock 5/16" and 3/8" Samson Amsteel Blue line in orange, dark green, and blue and can get other colors too. We custom make each and every line to order so we can make it however you want. We also don't look to make money on shipping - just cover our costs - so we can save you a few dollars there too. We deliver free to events, and you never know what kind of deal we will work you on a line!