for wood use 118 degree, for metal use 135 degree
split point drills tend to "walk" less when starting the hole
shorter drills (jobber or screw gun length) flex less and tend to wander less so they tend to drill a straighter hole.
there is a HUGE difference in drill bits and the additional cost for better drills are not just a way to charge more money.
depending on the material you are drilling
HSS (high speed steel) are generally the cheapest and least durable, cobalt (M4 with a little cobalt) are at the top end
carbide drills are for drilling hardened material and not suitable for everyday use as they are very brittle -- and expensive
a drill doctor is worth the money
that should get you started anyway..