To be honest with the low amount of current our tanks pull most NIMH batteries will do plenty fine and are a ton safer than Lithium batteries. However, if you are already familiar with lithium batteries they are a great upgrade. For those who aren't interested in learning how to charge, discharge, and store these batteries then stick with a nice NIMH battery and you should be just fine. I personally only use Lithium batteries as I have at least a few hundred lying around
I am constantly testing chargers and lipos are great for rapid charging and discharging (which helps put cycles and hours on the chargers).
Oh, I'm Erik btw. I'm with IMEX/Taigen so I won't be getting into X vs Y, I just wanted to offer my opinion here. I will say however to watch where you get your charger, most known brands are plenty fine but I've seen hobby shops burn down from incorrect settings (2 big name stores since I've been working at IMEX actually!). You would be surprised at just how often you mess up when inputting charge settings, especially when you are doing multiple batteries like I do. I'm super glad I get a cell check before starting a Lithium charge! In all honesty a NIMH will probably be more than you need and is simpler to maintain for most. Hope this helps!
Edit: One battery suggestion I highly suggest is to change the connectors. I am not fond of the Tamiya (aka Molex) connectors, they are hard to connect reliably and melt at around 250W or so. Nothing our tanks can accomplish stock, but a Deans connector or a XT60 is a nice upgrade IMO for reliability and finger comfort.