I'm in the camp of heated jacket liner. For me, that and heated grips are enough these days. When I used to ride long distances in 20F weather, the heated gloves were preferred. In the 40's on up, heated grips are enough.
Like Cycledude, my
Gerbing jacket liner is old school from about 2003 before things changed. Still going strong. That under Aerostich or Klim works very well. I use and prefer a
Heat-Troller from Warm and Safe for control. Infinite adjustment and best at power management. You can use a Heat-Troller with just about anyone's heated gear. And with heated grips! I run a mounted H-T with my grips. In the past I've run both mounted and the portables. I used to carry a portable just as a back up for the mounted unit on winter endurance rallies. They offer dual controllers too, for pants and jacket, gloves and jacket, etc. I found that pants/Jacket together worked fine, but gloves always needed a separate controller as I needed a different setting to be comfortable with the gloves and not over heat my jacket, or vise versa.
Now, a couple of points to consider:
Some jacket liners are wind proof, some are not. Wind proof is better.
Some jacket liners have their own insulation layer too, along with heating elements. If you're wearing the jacket liner around town when stopped for the night, this is really nice as it serves as a 'normal' jacket quite well. Uninsulated jacket liners are not warm enough by themselves to wear around at night if its cold. And let's face it, if it wasn't cold, you wouldn't have been wearing the heated jacket liner to begin with.
Any heated liner should fit snug to your body. Do NOT wear extra layers underneath heated clothing. A thin base layer or long sleeved tee shirt is best. (I like LDComfort) You want the heat close to your skin, but not on your skin. Need some extra? Put something over the heated clothing that presses it close to your body and is wind blocking. A cheap old school windbreaker works great if it's the right size. Too big works against you unless your riding jacket is pulling it tight to the body.
Now, about that heat control. You are aiming for "Not Cold". You do not want to feel "warm". If you feel warm, the heat is too high and you will start to sweat. When you sweat, every tiny drop in temperature will give you the chills. (liker dips in the road, crossing rivers, etc.) Which, in turn, will cause you to turn up the heat. Pretty soon you're at max and both baking and freezing and don't know why. This is where the infinite adjustment of the HeatTroller performs so much better than a controller with pre-set levels. You can perfectly dial in "not cold" and adjust as conditions change w/o ever being too hot or too cold.
Some riding jackets will allow you to zip the heated jacket liner in to it like the fleece or quilted liner. This is kind of nice, as you can don the jacket with only one zipper to deal with. However, when it's really cold, don't do this. The single zipper will bleed some air thru. Using both the jacket liner's zipper and the riding jacket's zipper means they don't line up exactly and you have a better block for any stray breezes. It will keep you warmer when it's seriously cold.
My old school Gerbing works fine for my needs now, but if I were in the market now, I would not consider wire technology. As CW said, the new FIR stuff is way better. The carbon fabric elements were a big step up from the wires, the FIR is a generation ahead of that. Gordon Gerbing makes his own stuff again, not with Gerbing brand.
Gordon's Heated Clothing
There is a ton of good gear out there. Poke around and see what looks appealing to you. The quality of Gerbing, Warm and Safe, Gordon's Heated Clothing,
Powerlet and others is first rate. Note that First Gear and Harley branded heated gear is made by someone else. Depending on the vintage, it could be Gerbing or Warm and Safe. Side note, don't buy a Gerbing controller. They stole the Warm and Safe design long ago and got a flawed version that has since been fixed. Heck, Gerbing may have fixed the flaw by now, but they don't deserve the business on those since they stole the product and reverse engineered it in China. Just my opinion. (I used to have some interesting conversations with the owners of Warm and Safe when I lived in Portland, OR.) Really good guys and very knowledgeable, helpful and would go out of their way to make sure you got your stuff when you needed it and got what you needed to keep you comfortable.
Sorry for the long winded reply. I used to think nothing of getting on the bike at midnight in 22F and riding from Portland, OR to Beatty, NV at the end of January for an endurance rally.
One last bit of advice: When ever you put on your heated gear, PLUG IN. That way when it gets cold enough to need the heat, all you have to do is turn it on.