I started with it on a Pi2 (~$70-75 with not-ugly case, power supply that's not cheap garbage that causes weird bugs to crop up, memory card), but I've since moved to a ~$150 Asus Chromebox (1.4Ghz dual-core Haswell Celeron) so N64 games will work at full speed (only mario64 worked well on the Pi2) and minor slowdowns in certain SNES games will no longer be an issue.
I find Lakka to be more stable and much lower-maintenance—for one thing I've never had to manually set up my controller with it, whereas Retropie required manual mapping, occasionally forgot said mapping, and of course adding a second (et c.) controller meant mapping again. Lakka's not as flashy (it only just got box art as an option, and it requires hand-adding files, no scraper, so I haven't bothered) but it's snappier and navigation is quicker/cleaner. Mimes the PS3 menu system, which is a very good thing IMO. Closest to a "just works" solution for under-the-TV console emulation I've seen.
Thank you for sharing your experience with it.
Should you decide to pick up that Asus Chromebox, I'd recommend following steps 2.1 and 2.2 on the Kodi setup wiki then running the easy setup script from the Kodi forums and using options 4, 5 (definitely choose to prefer booting from USB when prompted, will make updating/replacing Lakka in the future a snap) and maybe 6 to get its BIOS/boot system configured properly, then plug in your Lakka-installing USB stick. I don't know anything about Kodi and related stuff, but those are pretty much the guides to replacing ChromeOS on these things. I messed all this up and nearly bricked it, had to buy a $20 to-USB adapter for its internal solid-state memory module to fix my mistakes. Also try to have a Microsoft or Apple wired USB keyboard handy, the BIOS doesn't like devices that don't properly initialize in the amount of time they're supposed to (so, very fast)—most from those two companies do, many others, including lots of logitech gear, do not.
[EDIT] also, heads up: recent versions of Lakka include a rom/disk scanning system that only populates the per-system lists of games when the MD5 matches a "canonical" (archival project sets like no-intro, et c.) source, not (solely) based on file extension. Kick off the scanning with the rightmost section of the menu. Needs better messaging like warning when files don't match, but it works pretty well. You can still launch anything you want manually, and there may be ways to set it to the old only-file-extension behavior and/or add things to the per-console menus by hand, but I've chosen to clean up my files (n64 especially turned out to be... off) rather than investigate those options. A handful of systems (notably, arcade in general including CPS1/2/NeoGeo and a couple disk-using systems, most of which aren't great on the rpi2 anyway, if that's what you have) aren't supported under this yet. I've decided to simply not add that stuff until it's 100% supported rather than fighting it, since I've got plenty of other stuff to do, video games and otherwise, but to each their own.
There's an upstream bug preventing online updates and extra core downloading from working, too. Already fixed, likely will be released this month, judging from their typical pace of development.
Lakka worked flawlessly and I was able to get my library of games up and running with no hassle. My joypads (USB PS2 controller clones) didn't need configuring and seem to work fine - although I've only tested them for about half an hour.
Everything's not quite as responsive as an actual SNES, but it's the closest I've been on a Raspberry Pi.