Pinning engineering blueprints is great. Assuming you fully rank up an engineer when you unlock them, you don't have to care about flying out to visit nearly so often. And yes, you still have to go in-person to apply experimental effects, but an engineer who only does G1 blueprints on a module can apply an experimental to a G5-modded module, so you don't have to go all the way to the G5 engineer.
With that in mind, put some thought into what blueprints are most useful to you and where you can pin them.
This is based off of my pins, as a player operating primarily out of the Bubble. That means that Colonia engineers are pinned on the basis of particular expertise but not assuming that I'll visit them in-person. A Colonia-based player needs to plan in the reverse. I'm providing a broad base of options but will try to note where you may want to specialize.
Start off with engineers who have unique access to blueprints and pin accordingly:
Mel Brandon (Colonia) has the only G4 SCB (which is where SCB maxes). Pin the one you like best: Rapid Charge for PvP or Specialized for PvE is the common recommendation. Fallback: G3 at Lori Jameson (difficult unlock) or G1+experimentals at Elvira Martuuk. Brandon also has the only G5 FSD Interdictor mods, but the extra utility of G5 just isn't necessary versus a go-to pin elsewhere (see Dekker below).
Etienne Dorn (Colonia) has the only G5 Life Support. Pin Lightweight; it's the only life support mod that matters.
Liz Ryder has the only G5 Torpedo Pylon mod, but I prefer to use her for missile launchers below. Ram Tah has the only G5 ECM mod, but I prefer his more common modules below.
These engineers are unique by process of elimination, mostly because there are two options with one spoken for in the truly unique category.
Selene Jean and Petra Olmanova (Colonia) jointly have the only two Armor and Hull Reinforcement Package G5 mods. Pin Heavy Duty for each.
Broo Tarquin has the only remaining G5 for all of Beam, Burst, and Pulse Lasers (Brandon). Pin your favorite. I currently have Short Range Beam Lasers, but there are plenty of useful options.
Tod McQuinn has the only remaining G5 Rail Gun (Dorn). Pin the one you like best. While I use Long Range most often, I only ever feel like I need G1/G2 on it, so I've pinned Short Range as one that I might actually want at G5 occasionally.
Marsha Hicks (Colonia) has the only remaining G5 Multi-Cannon (McQuinn). Pin Overcharged, or possibly Short Range if you're sticking to knife-fighting ships.
Zachariah Nemo has the only remaining G5 Fragment Cannon (Hicks). Pin Double Shot.
The Sarge has the only remaining G5 Cannon (Hicks). Pin your favorite. I have Overcharged.
Bill Turner has the only remaining G5 Plasma Accelerator (Dorn). Pin your favorite. I have Efficient.
Liz Ryder has the only remaining G5 Missile mods (Olmanova). Note that fixed and seeker missiles pin jointly. Pin your favorite. I have High Capacity.
The Dweller has the only remaining G5 Power Distributor (Dorn). Pin Charge Enhanced.
Bris Dekker has the highest-remaining FSD Interdictor at G4 (Brandon). Pin Expanded Capture Arc.
Hera Tani has the only remaining G5 Power Plant (Dorn). Pin your favorite, or at least the one you expect to want at G5 the most frequently (see Quent below). I have Armored.
Didi Vatermann has the only remaining G5 Shield Booster (Brandon). Pin Heavy Duty or Resistance Augmented, whichever you think you'll use more. I have Heavy Duty.
Lei Cheung has the only remaining G5 Shield Generator (Brandon). Pin your favorite; I can make a case for Reinforced, Enhanced Low Power, and Thermal Resist, and it never feels like I've picked the right one to pin. I currently have Reinforced.
Juri Ishmaak has the only remaining G5 mine launcher (Olmanova), but I prefer to pin Sensors on him later.
If you don't care about Cannons (I really don't), you might move Sarge to a limpet controller (Lightweight). If you also don't have Colonia engineer access, you might put Rail Guns at Sarge and Multi-Cannons at McQuinn, accepting the loss of a pinned G5 Rail.
These engineers aren't strictly unique but are still straightforward to allocate.
Professor Palin and Chloe Sedesi's highest option is G5 Thrusters (each). Pin Dirty at one and another (probably Clean) at the other. You could skip unlocking Sedesi, but her requirements are identical to Palin's, so you might as well do them together. I use Clean thrusters on smuggling ships, so there's utility for me to pin both.
Marco Quent's highest option is G4 Power Plant. Pin your second-favorite, or one you might use most but rarely if ever at G5. I have Low Emissions.
Elvira Martuuk and Felicity Farseer have the other G5s for FSD (Brandon), and you probably only need to pin Increased Range. The choice of which to pin, then, comes down to what secondary non-G5 pin you want to allocate. I have Increased Range pinned at Martuuk.
Left to designate are: Farseer, Ishmaak, Tah, Jameson, and Fortune. Key modules not pinned include the DSS, any limpet controllers, and most utilities. The process now becomes largely a matter of preference.
Felicity Farseer is great for applying experimentals but not particularly useful for direct engineering. I pin the G3 DSS Expanded Probe Scanning Radius here as I find that G3 is more than sufficient for common purposes (i.e. getting the efficiency bonus on non-gaseous worlds).
Lori Jameson and Juri Ishmaak both have G5 DSS and G5 Sensors. I use both Lightweight and Long Range sensors regularly, so I pin both with these two engineers. If you don't use both, you might want to shift one of these to the DSS. You might then shift the FSD to Farseer and put Martuuk on a secondary Shield Generator.
Fortune has a lot of utilities and utility optionals; pin your favorite. I have Collector Limpet Controller Lightweight. I might extend the above case and shift Fortune to Sensors, Jameson to DSS, Farseer to FSD, and Martuuk to the Shield Generator, but I like quickly shaving some mass from mining ships and limpet controllers never need experimental effects so this is a zero-travel pin.
Tah has the utilities that Fortune doesn't and the sole Bubble source for all of his G5s; pin your favorite and recognize that you're going to have to travel for the rest regardless. I have Chaff Launcher Ammo Capacity. It's not even a G5! But it's commonly useful. Lightweight Heat Sink is the other one I might consider.
I hope this gives you a starting point for your own pinning process. While your preferred playstyle will impact what and where you want to pin, I hope the exclusivity-based approach shown will help you narrow the choices to manageable ones.
As of early 3307, Colonia-based engineers have the full set of max-grade blueprints (SCBs still max at G4). So there's no real effort at all for this! Pin whatever you use most often in the Bubble and go wild with your Jaques-adjacent pilot.