They are both awesome quality jackets with the best customer service. I'd have to go with Simms though if I was to get another to replace my SST 7 yr old jacket that is still going strong and bullet proof. Reason being is because Simms products are designed strictly by Fisherman for fisherman out of Montana. G3/G4 is next. Yes the fleece pockets in the upper rear of the SST chest pockets are awesome, but kinda uncomfortable when you have 9" size fly boxes in them.
I have 4 sets of the Simms jacket and pants that we use for our clients. It's the Pack Lite design.
They've held up great for the last 4 years.
Of course in Hawaii, we don't have to deal with the cold, just the rain.
I ponied up for my first quality fishing jacket in 2006. I went with the SST because it was less "techinical" looking than the Simms at the time. No complaints. Many days of comfortable fishing in nasty conditions. My only suggestion would be to try them on before you buy. Sizing can be quite different between the two companies.
There both junk. On the OP, if ain't rubber, its going to leak! I have had several different kinds and all with out exception start leaking with in a year, or in some cases less! A LOT LESS! I bought a cheap Leakman (hodgeman) and throw it in the wash about every two months. Then fill it with newspaper, hang it upside down in the shop and spray/soak silcon water proofing all over it. Works perfect. You don't look too Eddie Baur when hooking a 17lb. buck in a blinding rain storm, but your dry.