Selecting a transistor, is there a go to transistor for typical projects?
Yes, there are some common general purpose transistors, based on current handling. These do not take into account bandwidth (e.g. for RF appications), or high voltage (>30V).

BJT


2N3904/2N3906 (SMD MMBT3904/MMBT3906) (upto about 100 mA)
BC547/BC557 (higher gain than 3904/3906, lower current)
2N2222/2N2907 (upto 250 mA)
BD139/BD140 (upto 1A)
TIP122/TIP127 (darlington; upto 3A)


Current limits are conservative, about half of what datasheet says.

MOSFET


2N7000 (SMD 2N7002)
BSS138 (logic level)
AO3400/AO3401 (not that common, but very useful)
IRFZ44/IRLZ44(logic level)/IRF4905 and IRF540/IRF9540