Now with Transformers 4 being considered as his last film, Michael Bay needs to focus on including the right and best kind of vehicles and aircrafts for new autobot and decepticon characters to transform into other than small and lousy cars. Vehicles he should choose are jeeps, suvs, trucks, jets, choppers, anything except a small car (unless they are females).
First off, the Autobots
Override
Hound
Trailbreaker
Powerglide
Ultra Magnus
Windcharger
Moonracer
Springer
Silverbolt
Fireflight
Skydive
Slingshot
Sky Shadow
Omega Supreme
Now for the Decepticons
Skyquake
Blitzwing
Cyclonus
Scourge
Octane
Thrust and Dirge
Onslaught
Vortex
Treadshot
Swindle
Blastoff
These are the best kinds of vehicles and aircrafts that Bay should consider including as robots. Sure, he does need the vehicles and aircrafts to be filmed physically on set but does he do that for all of them. No. He was able to include these means of transportation digitally in the previous films so it shouldn't be a problem for him to worry about. Some of the new characters may replace some of those from the last movie due to certain reasons, complecations, etc. Bay didn't include vehicles like these in the third film because he was in a rush to end the franchise with only three. But now that he is up to doing a fourth film, and is putting the fifth on hold for someone else to direct, Bay shouldn't have any reason for not choosing bigger cars, and awesome jets and choppers.