In Puerto Rico, and from all the TV from other countries I've heard, you'll almost always see "Voy a comer" over "Comeré", for example. When someone uses "Comeré" it sounds like either an answer to a question (which, obviously, is an ok use) or a strongish assertion. But it's very dependent on the situation... Say you're arriving late to something, I'm more likely to text to my friends "llegaré pronto" than "voy a llegar pronto". The second one sounds dry and almost passive-aggressive. But, for more common things, I think ir + a + infinitive will probably be your best bet.

Well, I'm not a native Spanish speaker but I'll summarize what I learned in Spanish class. The "ir + a + infinitive" formula can mean "will do sth" or "going to do sth" depending on the sentence. There is another future tense that has the "infinitive + á/ás/emos/án" formula. This always has the meaning of "will do sth". The conditional tense is similar to English. This has the "infinitive + ía/ías/íamos/ían" formula. Depending on the verb, it can mean "would" or "could". Sometimes you can even use the simple present tense to indicate things happening in the immediate future. This tense can also replace the present progressive. I hope a teacher or a native speaker can give you a better run-down.