I have been using an Epson V700 since 2008, and a Nikon Coolscan V since last year. Even though they are not the exact same models you were considering, they are similar in principle. And here are my perspectives
1) Flatbed vs dedicated 35mm scanner
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Format support: obviously if you shoot medium format and large format, you have to have a flatbed.
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Quality: for 35mm film, there is clear advantage of dedicated scanner in terms of dynamic range and resolution. I use 3600 DPi for Coolscan, and 2400 for V700. For 120 and large format, flatbed is more than good enough unless you do wall size prints. My buddy Jan scans in 4800 DPi for his flatbed (Microtek M1 Pro, which is similar to V700), and then downscale to 2400 dpi in Photoshop using the bicubic sharper option. He said he got better results than just scanning at 2400 DPI. I tried it but the results were inconclusive.
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Convenience: definitely more convenient with V700, since you can load 24 frames of 35mm at a time and let it run automatically. So two feeds per 135-36 roll. My Coolscan V only takes 6 frames at a time, so I need to feed 6-7 times for one roll.
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Scanning speed per frame: I have never timed them scientifically, but they are comparable when set to appropriate DPi and quality
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Film flatness is more important than anything else, otherwise all those precision optical / digital processing is for nothing.
2) Scanning software:
Even though I use Macbook mostly, I have a dedicated older windows 10 PC as my scanning station.
In my humble opinion, both the factory software are quite good and I don't think it is necessary to get 3rd party. I use Epson Scan with V700 in Professional mode and Nikon Scan for Coolscan V. They are simpler than Silverfast Ai or Vuescan, and more user friendly to get high quality results quickly. I have tried both Vuescan and Silverfast Ai in the past: their learning curve is substantially steeper. And in the end, the results are not necessarily that much better.
For B&W and color slides, I don't see any reason to get 3rd party software. For color negatives, there might be some advantage of Silverfast Ai since you can calibrate and fine-tune individual profile for each particular film stock. My buddy Jan swears by Silverfast Ai for that reason. But for me, I just shoot a few frames with a X-rite colorchecker and then adjust in Lightroom post-scanning. I shoot a mixture of many different film stocks, some of which are expired, and in different lighting conditions. So it is actually easier to adjust roll by roll, instead of say one Fujifilm Reala 100 profile for every roll.
Conclusion for me: If I can only buy one, I will go for the flatbed. If I can afford it, I will buy both the flatbed and the dedicated 35mm scanner. Ideally I can upgrade my Coolscan V to Coolscan 5000, which can scan one whole roll without re-feeding, but that is a convenience luxury at several times the cost.
Recommendation for you @Richard Jepsen : since you are entirely 35mm B&W, I would probably go for a dedicated 35mm film scanner to get the most out of the film. In addition to the new scanners, do consider the Coolscans. I got my Coolscan V for about $500 locally, in excellent condition. If you are short in time to get everything scanned, a Coolscan 5000 with the bulk loader might be your best bet.
