Depends on what you want. If you want the sound you used to be able to get pushing the drum bus against a tape machine, u-he satin or Softube Tape. If you want the sound you used to be able to get from your four track recorder with a lot of controls for saturation, warble and noise floor Goodhertz Wowcontrol is hard to beat. There are a lot of others, too, and I think I might have them all, but these are my go-to.
Looking for one as well. From my short investigation TB Reelbus, BRA Magnetite, Slate VTM, U-he Satin, J37 and Overloud Tapedesk imo are on the top of the list for saturation purposes. Reelbus however seems to be the real pretender.
Then we have also RC20 and Klevgr. Dawcassette for more sonic creativity then strict emulation. I use the first one and cannot praise it enough.
In the end ToTape5 and FerricTDS are very interesting free alternatives.
If you have UAD though I think you already have very high quality emulation.
P.S. Not strictly tape but Soundtoys decapitator is on sale now.
I am generally looking for the compression/saturation effects of a well maintained tape deck, and to that end I use the UA Studer and Ampex plugins, the Softube Tape plugin, and u-He Satin. They all sound different, they are all capable of that subtle tape effect that I am looking for.
I've been using the UA plugins pretty much since they were released, so I have a certain familiarity with them that helps.
When I am working in Studio One I place the Softube plugin in the master slot - it is a fantastic workflow, and it works well for me.
I've only recently picked up Satin, I really like how it sounds, but that the moment I tend to use it as a delay or flanger more than as a tape emulation. That will probably change over time.
I have tried several others, but it would have to be pretty darned cool to move me to add another tape emulation plugin, I'm happy with what I have. That's not to suggest that the others are not as good - just that I am both lazy and cheap!
I have Slate VTM and it works. Waves MPX is ok too. I would love to grab Softube Tape or U-he Satin but that's just too many tape plus.
Another secret weapon which is SoundToys FilterFreak. You can engage the 'analog modeling' function, with various settings, with the filter wide open, and it does some nice stuff with analog saturation, compression, transients, etc. It is not subtle but can be absolutely amazing on a given track.
Good Bus compressors are useful for this effect as well. TheGlue, bx_townhouse, SSL, bx_VSC-2, etc. stuff that gives character. SoundToys Decapitator. Softube stuff.
As pointed out up thread SoundToys is on sale right now.