Can’t comment on 45Drives and the ASRock Rack and Supermicro are in different classes. Both are fairly affordable, but the asrock rack are mostly prosumer gear, while supermicro are enterprise. Despite that, I’d rather look for the feature you need, more than the brand, if your only choices are those 2.
Are you running a homelab or homeprod? If it’s the latter, you should optimize everything to the max and run it on 1 or 2 odroid h3’s, or a ryzen 7700 (non-X) build if you need the additional oomph.
I prefer suggesting builds based on workloads, which you haven’t provided. Homelabs can be ran on power hungry 45D or R730, as long as you don’t run thenm 24/7. I run my threadripper 1950x once in a blue moon, when I want to test something, or when I power my windows VM. But everything else, I run on my thinkpenguin 4 bay NAS with an i5 T-series 6 core 11th gen CPU (not that I have much right now, I’m still testing the hypervisor).
My NAS is a pine64 rockpro64 (and the thinkpenguin one, but that’s nas and hypervisor dual-purpose). I also have a container SBC (odroid n2+) and a backup server (odroid hc4).
Examples of what I’d be running are just local DNS’es (unbound recursive and bind9 authoritative), DNS sinkhole (blocky), NFS, matrix server (dendrite or conduit), jitsi, gitea, zabbix or prometheus + grafana and other lightweight stuff (like a static site generator and maybe android VMs). Potentially thinking of hosting a peertube instance.
These are just examples, but the i5 is more than enough to host the above and I could probably host everything besides peertube, matrix and jitsi on the odroid n2+.
What’s your workload going to look like? I assume if you are upgrading, you already have something running.