Finding the perfect emulation for your needs is a complicated path, but not impossible. It depends a lot on what you want to do as there is not one solution that fits them all. Do you want hardware compatibility for games, demos and touchy apps? Do you want the fastest and modern look and feel for GEM productivity apps ? Do you want an easy solution?
If you want a plug and play solution, you should give a try to AtariX, which is the open source version of Magic Mac : viewtopic.php?f=28&t=33296&p=349493&hilit=atarix#p349493
It's fast, compatible with all well written GEM apps, in a nutshell it's Magic ... but it's not an hardware emulator, so forget ST games, demos and many non gem softwares.
If you want an emulator as close as possible to the original hardware you have Steem and Hatari. I don't know the first one so I'll let the expert talk about it, but I know and use Hatari. Hatari can emulate ST and STE almost perfectly allowing games, demos, midi apps ... to run. TT and Falcon emulation are still a work in progress. Falcon emulation is working quite well indeed.
Now, there is an issue with Hatari above 2.0 : when using disk image for hard drive, the desktop.inf or newdesk.inf from the hard drive image is not used ; instead is used a standard one. Look at this thread for a temporary workaround or use Hatari 1.9 which doesn't suffer of this bug.viewtopic.php?f=51&t=33129&start=125
Aranym : this a special animal, as it doesn't emulate an existing machine. It's a kind of hybrid Falcon / Milan, booting only with emutos, Tos 4.04 or straight into Mint, emulating most of the Falcon hardware (DSP, midi and audio are not complete) with a 68040 under steroid (I got a 4Ghz equivalent 68040 with a fast Core i3) and with access to the host hardware. That's my favorite of all, but it can't be compared with Hatari as it is much more powerfull but less compatible, so forget games, demos and touchy apps. Small, detail, it's learning curve is kind of steep and first contact can be discouraging.
I have build a distribution for it, ready to install, it's EasyAraMint : https://sites.google.com/site/emaappsarch/home
Aranym can be also configured to boot from standard TOS4.04 with Videl emulation and use Videl Inside to have hi resolution in 256c and 16bits colors. I can share you a disk image ready to use, which runs Calamus, Photoline, Das suite ... and many others if you are interested.
Finally, you have also 2 self booting distributions, BeePi and BeeKey, which are full system, the first one for RaspBerry Pi and the second for X86 that boot directly into Aranym (EasyAraMint) an allow to transparently launch games, demos or hardware sensible apps in Hatari (see previous link).