I thought it was best to buy both - when on sale. I'd probably go the FabFilter route if starting again and had the dosh but there's nothing wrong with either of them.
The singles in T-Racks are useful as well as being used as a whole. There's also a 'How To' video on T-Racks mastering that's about $5.
Ozone is to be used sparingly (I have 4, which is like 5 but has different colours. Colours don't change the sound. They make things look different). The temptation is to whack on a preset and 'Ooohh' at the new loudness and punch. It's best to learn how to actually use it and then you can fine tune it. There's a number of videos flying around about Ozone too. Even if it's about Ozone 4 or 3, the principles are still the same.
Of course, buying Ozone 5 can lead you into temptation for Alloy 2 on individual tracks.
When you have two you're looking at and you think you may end up getting both then buy each one when they are on sale. You can pick both of these secondhand too.