I went with my tutor to BIG center, to search series starters for my 2x8W T5 bug-zapper.
In Machsanei Teura, we found generic blue transparent Neptun FS-2 series glow starter, which have a one U folded contact.
In ACE, we found Philips Ecoclick S2 and Osram ST151 series glow starters.
In both stores, I couldn't test the starters, as the stores had no stands and fixtures for testing 2x18W T8 on a single 36W T8 magnetic ballast.
Which of them preheats the electrodes better, and have the least flashes during operation, so causes the least sputtering to the lamp?

I don't think there would be any systematic difference. If you observe some differences sometimes, they would be rather random across products of both makers.
And moreover the bug zapper won't be turned ON for only short time, but for many hours per single start. Then the vast majority of the lamp wear come from the burned hours alone, so the preheating play very minor role.
So in your place I would grab the first ones come to my hand and continue with other business you would have there...

The glowbottles of 3 starters, as far as i can redraw from memory, are pictured here

Nepton ones have the same slim Christmas-light shaped glowbottle, same as most Korea-made starters had for ages, back to the days of metal-can starters. The exact same glowbottle design thats in this Nepton, is used in all of the following starters you can spot in Israel : Samsung, Orlite/Orlight (early models), Elita, Champion/OrAd (early models), New Star, Sure Star, Luster, maybe Taylon, Prestige, Gerustar (early models), General (last model before the recalled ones) and i might have forgotten something

Experience with the FS-U ones (S10-equivalent) of those (from the metal cans in the 70s to the modern ones) shows that they have pretty big spread. While some of them last for ages (the metal cans with small hole, of which quite a few are still in service, and there were more of them not many years ago) are either OrAd which i know to be the same glowbottle, or Taylon which i suspect to be the same too), few get stuck over a few years for no apparent reason and looks like the glowbottle itself is what gets stuck but i cant tell for sure if thats the common failure mode cause i only tested one (by removing the capacitor and trying to reuse it)

The Osram and Philips appear to last pretty well, as long as not treated badly (left with EOL lamps etc), so they are a close match to the Nepton and the likes of it

One thing i dont understand is this : In most S2 equivalent glowbottles (yet not in hte Philips S2 itself), there is usually a solid metal pellet welded to the static electrode. I dont have a clue what it is for. My guess is htats its a small thermal capacitor, meant to heat up and keep the bimetal warm for a while longer (as long as it touches it), so that the starter have a bit longer delay and waits for the other starter to close, but realy its just a guess



Now Dor, this is a task for you : Go to places (preferrably ones with 90s legacy, those usually have variety of starters), identify the brand of starters used, play with the switch, and see how much flashes it takes to start a lamp with either starter brand, this would give some evaluation on what lamp life to expect from a starter with given glowbottle type and fill

So here is the complete (that i can tell by memory) list of starters that i seen in Israel and what glowbottle is inside :

Cylinder IU Starters :
Prusman (metal can with big round hole) - late 70s to 1980 - some argon fill, some mystery cyan fill
Canmo Light (metal can without hole) - i think 70s - unknown fill
Solex (transparent blue plastic, horizontal etch) - late 2000s/2010s - argon fill
King (ordinary white plastic, blue etch, company name writen in white on blue) - 80s - unknown fill
Or-lite (with "-") (transparent blue plastic) - late 2000s/2010s - argon fill
Hyundai (transparent blue plastic, horizontal etch) - 2010s
Eurolux (white plastic, eurolux written around top) - late 2000s/2010s - mystery cyan fill
Osram (look same as all 111's - have to open it to tell) - tiny batch in the early 2000s, rare - mystery total white fill

Starters with their own designs :
Philips (all models of S10 at least from late 80s) - see picture
Osram (all models with the tapered end case, som of the earlier ones too) - see picture
Narva BSt65 (side etch, wide ridges on head) - 90s/2000s - thicker Christmas bulb with contacts reminding of the Korea ones and IU ones, mystery cyan
SKL FS-U (side etch, bold font) - 2000s - thicker Christmas bulb with contacts reminding of the Korea ones and IU ones, mystery white, very fast acting
Champion (only small part of those with black circle on M in the etch) - 90s - same as SKL but neon filled

Christmas light starters - presumably Korea made - all with mystery cyan fill :
Samsung (typical white plastic starter) - 2000s
Orlite/Orlight (without "-" after "Or", white plastic, horizontal etch) - early 2000s
Elita (red color etch) - 90s (left aligned text in etch) and early 2000s (centered text in etch)
Champion (only ones without black circle around M) - late 80s, early 90s
OrAd (metal can with small round hole) - 70s
New Star (typical white plastic starter, etch text in bold) - 80s
Sure Star (red color etch with symbol instead of company name) - 80s
Luster (company name in cursive) - early 90s
Taylon (metal can with small round hole) - 70s
Prestige (ordinary white plastic, blue etch, company name writen in white on blue) - 80s - unknown fill
Gerustar (sans-serif font etch) - early 90s
General (company name in etch in small font, last model before the recalled ones) - 80s

Random blob shaped glowbottle (starters often come stuck straight from the factory, often vacum losses in glowbottle), allways neon fill :
Champion (etch with black circle on M - most of them) - 90s
Luxten - 90s, early 2000s
Wen Tai (horizontal etch) - 90s, early 2000s
Sun (black etch and blue etch) - 90s
Gerustar (the ones with serif font) - early 90s



So here are the glowbottles of the three (Nepton, Osram, Philips) in S10 and S2 equivalents - shown in cold and hot (closed) states

@Ash: The time necessary to heat up the starter for it's close cause only user annoyance, as during this time the lamp is not yet preheated.
After the starter close, the contacts usually weld together and the strength of this weld then determine, how much force is necessary to break it open, so how low the bimetal have to cool down, so how long would be the preheat time.

Without this welding (when the starter is new), the starter cycles very fast, so let the lamp ignite with cathodes not yet warmed up enough. Many new lamps ignite even with rather cold electrodes, so even the first cycle become the only one. But that mean the electrodes wear out because of the cold start.
But once the weld start to form, as other side effect it alter the contact surface, so each time the weld become different, so does the preheating time. This is then the main reason for the high variations in preheat time among individual pieces...