I have both - the 7300 for HF and the 991A primarily for VHF/UHF. Ergonomically, the IC7300 is by far the nicer radio - an excellent screen and controls that are well thought out and well placed. The 991A suffers from the usual Yaesu disease - a horrible front panel design that looks "exciting" in the publicity shots but soon proves to be a pain to operate! That said, both my radios form part of an integrated, computer controlled shack and I never touch any of the front panel controls, so I really don't care too much about the layout....
In terms of performance, I think things are less clear. On paper, at least, the 7300 has the more modern architecture with direct sampling SDR - all signal processing is digital from the pre-amps backwards. The ICOM filtering with its twin passband tuning is certainly very good - you can shape it almost any way you want and it is very sharp. The wide-open front-end can be a problem in the presence of strong adjacent channel signals and the 7300 can overload relatively easily. I live in an environment where any signal over S9+20 is very rare and this does not cause me any problems, but it certainly is a problem for some users.
The 991A is a more traditional superhet with a 3kHz roofing filter early on in the chain and that provides a lot of protection from strong adjacent channel signals. It digitises the signal at a 24kHz IF and applies DSP at that point. This is actually a very similar architecture to that of the FTDX10 that everyone is raving about... In the 991A, they call it "IF DSP" and in the FTDX10 it is "Hybrid SDR" - but it is unclear to me just what the difference is. Yaesu have always understood noise reduction better than ICOM and this applies to the 991A vs. 7300 debate. The DNR on the 7300 is good and will reduce hiss and general background noise a lot, but the DNR on the 991A will often remove it completely - at the expense of introducing artefacts of its own to the received signal. These are the sounds that some refer to as "dripping" or "trickling" - they are usually low level compared with the received audio and I can live with them if they help me get another DX QSO in the log, but they seem to annoy some people quite a lot!
One possibly significant downside of the 991A is its narrow maximum receive bandwidth. That is determined by the 3kHz roofing filter and nothing short of a replacement filter is going to change that. It's a fine choice for telephony, but most of the world has gone FT-8 these days and the FT-8 channel seems to get wider every month. 3kHz is really too narrow these days - even the 3.6kHz maximum of the 7300 is looking a bit narrow. If you put a 991A on the standard FT-8 frequency and never retune it, you will miss signals that are sitting up above the 3kHz mark - you will not even be aware that they are there. The FTDX10 has added a 12kHz roofing filter which should address this...
The bottom line? I've had the 7300 for several years now and I'm very comfortable with it - like a well worn pair of shoes. It is still my primary HF rig, but the 991A - which I bought a couple of months ago as a VHF/UHF rig - has pleasantly surprised me. It's a pretty unpleasant radio to use from its front panel and the spectrum scope is poor, but my radios are always operated from the shack PC and I use an SDRPlay SDR receiver as the spectrum scope displaying on a large monitor. In terms of actual RF performance it is pretty good - sometimes better than the 7300. If I had bought it first and learned to use it properly, it is quite possible that I would not also have bought the 7300. If you are not a dedicated computerised shack sort of person, then you really should try to get some hands-on time with a 991A before handing over your money - I would find it a difficult radio to love if I were having to operate it from its front panel.
Martin (G8FXC)