I assume you are talking about the pushrod 500 singles? I think the "Electra" was the Swan Song of the Pre-Unit. It had the nice gear oil pumps, a crank-triggered CDI, working electric start, the new 5-speed and a front disc brake. I believe the crank had a needle bearing con rod also. All the stuff that many owners were doing to the Pre-Unit Bullet anyway. It would be my 1st choice.
The UCE should be an even better daily driver, but you'll need to bulletproof the fuel pump with supplemental filters and defang the auto primary chain tensioner so it doesn't overtighten. Other than that it has all the bells & whistles. The EFI works well (usually) if you keep out the solids. "Normal" tank rust is a killer on the EFI. You can always retrofit an Amal with the H's conversion, depending on where you live of course. A 10 micron filter easily keeps out carb-clogging solids, but the UCE's EFI needs way better filtration, likely 5 micron or less. If you could get the fuel pump out of the tank it's be easier to keep it alive with a real industrial pre-filter.
I like my '99 Pre-Units, but they are fun machines for me, a window into back to the 1950's. The ratios of the 4 speed determine your pace. The engine won't be hurried, and if you do it's at your peril. The hardware determines a large fraction of the pace of ride. The UCE & Electra are less so, more "Honda-like" in their usage, a bit more "gas 'n go". Their "Electric Leg" gets more important every year, eh?
My red Bullet, Krasny Oktobyr, sports an alloy barrel, forged 6.5/1 slug and H's "sticky" front brake shoes. The barrel was really worthwhile for me in SoCal, as was the forged slug. With 110 degrees Fahrenheit ambient summer air temps, heat rejection capacity is now increased, piston reliability concerns are reduced, and I can now stop reasonably. All the cables are H's H.D. variety and it makes a noticeable difference in feel & function. The transmission was converted back to right hand shift to eliminate the bodge. This was both a functional change and a retro preference. Right side shifting is an acquired skill for predominantly Japanese-machine riders, lucky for me I live way out in the sticks.
But if you weren't talking about the pushrod 500's, I'd get the Himalayan. It's a user-friendly clean sheet design, easy to live with, keeps up with the traffic we're likely to encounter, & a bit lighter than the Interceptor. The trail geometry & suspension soaks up jolts from potholes & random road debris better. I'd save up the cash and have an H's 460 kit setting around for whenever I felt the top end needed attention, and make a good bike even better.
If you are primarily a highway/road rider and the weight isn't a concern, obviously the Interceptor is the way to go. 47+ HP, a 6-speed box and good road manners make that no contest.