There are indeed a lot of different software.
If you want a HUD, I would definitely recommend Hand2Note. It is probably the most powerful tool for that at the moment. And it is free for NL25 and under. However, if you haven't ever used a HUD and your skill level is not very high, you could find it difficult to use H2N at first. That is because there rare not so many stats readily made so when creating a hud, you maybe need to create some stats on your own.
If H2N is not for you and if you get HM2, you will get a free upgrade to the upcoming HM3. That might be better than the current PT4, so I would get Holdem Manager instead of Poker Tracker.
When it comes to Jivaro that Vorpal mentioned, I think it only works at PokerStars. It also advertises positional awareness of the HUD, but I believe pokerstars banned those. The free trial lasts only one month and then it seems to be 5$/month so could get more expensive on the long run. The software looks beautiful and simple, but I think it might be even too simple.
About that fun software Sidekick: it is not updated or maintained anymore so it could just stop working at any minute if the poker room makes some changes. And there have been already problems reported that it doesn't work.
Equilab you definitely need. The free version is just fine.
If you are just starting out, I think those are the software you need, a tracking software and equilab. When you start working on your game more and get more knowledge you can consider software like power equilab, flopzilla, gto solvers, pokersnowie and so on