Re: better, how?
Over the past year we've inherited a lot of HP kit, and we're mainly a Dell shop. So I've got to see things from both sides. We have 3rd party hardware support, so I can't comment on any differences there.
We run a mish-mash of RHEL/CentOS and both Dell and HP provide firrmware updates for (Enterprise) Linux distros. I would say that HP's SPP/MCP is probably a bit more distro-friendly than Dell's OMSA, but they will both do RHEL and SUSE based distros.
From a firmware point of view getting hold it it (via the web) is easier for the Dell kit, as getting any info out of HPs website can be hit and miss. I also prefer the Dell OMSA method of getting a running server to update itself, rather than HP's SUM (I think) where you have to register a server and push it out. On a brief play with the latest version of SUM I found it to be quite dumbed-down and not as forthcoming with information on what you're pushing out to where.
For a one-off (ISO) boot firmware update I much prefer HP's Smart Update DVD than anything from Dell. Mainly as the HP method actually manages to update the lights out card you're probably using, whereas the Dell versions don't.
Which brings me on to lights out cards. Dell's DRAC offerings have improved quite a bit over the years, and iDRAC7 is pretty good. They must have been looking at HP, as now for the 'Enterprise' version where you can use the dedicated LOM port, a license is needed. Though I'm pretty sure you can still use the console, unlike HP's iLO3 where that's what you need the license for. With the iDRAC7 I'll say that it seems to have a better awareness of the other hardware in the server. So before you might have to run up the OMSA front end to see what was going on, but this (or a lot of it) now seems to be integrated into the DRAC, whereas as far as I know you'd have to fire up HP SMH separately.
One thing that HP iLO is still better than Dell iDRAC is the actual console. They both use Java to do all the hard work, but the iLO console is pretty rock solid. The iDRAC is still very flakey and will freeze/dropout at the most inopportune of times, usually on CentOS when the kernel selection screen kicks in...
On reflection, I think I slightly prefer HP kit but Dell isn't that far behind.