Help with finding pod-based Coffee and Espresso maker
The manufacturers of the machines and the coffee partner to make use of brand recognition. So I could buy Costa brand (2nd biggest coffee shop chain in the UK) for my Tassimo, but if I wanted Starbucks I'd need a different machine. Nespresso is part of Nestle so they're not going to licence rivals to make pods for their machines. The choice you can easily buy is as important as the overall range - while you can get the pods delivered it works out expensive. Pods from different manufacturers are completely incompatible, and these machines don't take normal ground coffee without hacking the packaging. 

I've used a Nespresso and a Senseo and have a Tassimo (that I no longer use because the coffee is expensive and wasteful on non-recyclable packaging). Neither makes espresso, despite labelling. They make a reasonable imitation of a weak espresso. The nespresso is slightly better in that regard, or a Tassimo that allows you to adjust the amount of water (so not the most basic). But a moka pot is closer to espresso than either. Some also do you chocolate (though not very well); I'm only keeping my Tassimo to use that up. 

Pretty much any pod machine that says it can do espresso can also do plain coffee. Overall you need to pick one for which the biggest range of suitable pods is available easily. Suitable depends on the user.