Lee is right in a way, the 817 is a more specific radio than the ones he's listed. It's main use is QRP portable and bordering on light portable. There are better options for ultra light portable but they are nowhere near as band or mode nimble, usually being one or just a couple of bands and generally CW-only.
How much hiking and how far are you thinking? Is it's use going to be mostly at home or out afield?
The only competition IMO is the Elecraft KX-3, which improves on the 817 by dissipating 10W and being more frugal with RX power. If there is one complaint I have, it's that the FT-817 draws much too much power when just listening. But OTOH it's a decade-old design and so I would expect new competition to target obvious weak points. The KX3 I believe is in the 100mA range on RX. The FT-817 interface I still think is much nicer and my impression is the Yaesu feels more solid to me. The Ten-Tec Argonaut and now discontinued ICOM IC-703 are also potential options for light-ish HF rigs.
The FT-857 and TS-480 require at minimum an external battery and the FT-897 internal battery alone weighs more than the FT-817. All are larger, although the FT-857 isn't a whole more. I would call those three radios backpack-able in that you can put the radio, a battery, tuner, antenna and log book in a backpack and take it some place, but that's all that you're taking. I can pare down my 817 kit to a single band dipole made with 24AWG wire, the radio and a log book. All of this fits in a surplus military pouch in the top of my backpack, leaving plenty of room for the tent, bag, stove and extra clothes in the main compartment. Even if I take a little solar panel and my Elecraft T1 tuner the packed size doesn't bother me on a week long hike. No way I would drag a 480 or 897 on more than a day hike.
Do keep in mind that the internal battery on the FT-817 isn't going to give you a lot of time. I find that at 5W I can transmit intermittently maybe an hour or two and listen for a few more. It's enough to take backpacking for a weekend where you might operate once or twice briefly after dinner.
Nice thing is a 5A-hr pack does last a really long time and if you build one with lithium it wouldn't be heavy. However if you look at the spec the FT-857 draws just twice the power on RX (0.55A squelched compared to 0.25A for the FT-817) and not a great deal more transmitting at 5W. Of course the FT-817 can go down to 0.5W where the lowest you can go with the FT-857 is 5W. Point here is that the 857 isn't a whole ton bigger and you can operate QRP with the upside that you can go QRO if 5W isn't cutting it or you absolutely need to make a contact. I personally wouldn't want to carry a 857 for long trip, but it's not so large as to be impossible.
Antenna, I assume you mean portable. I do a 44 foot doublet made from computer ribbon cable, the so-called NorCal Doublet. This works well with that little Elecraft tuner and is pretty small and light. I also have a Ventenna HFp that I like alright, but it's more bulky and fussy to set up. But it's a vertical and that changes propagation.
