I have a "comfort"-type bike that came with grip-shifts and it was difficult to ride hard without inadvertently shifting the gears. Putting on some trigger-shifters was the best thing that happened to that bike.

That said-
The cheapest shifters are grips--the bottom-line Srams now are only about $15 a pair. They shift very poorly, yet these get stuck on a lot of cheaper (sub-$500) bikes as OEM parts. The cheapness may be a bigger problem than the shifter type.

When I switched to triggers I went to the next-up level, that cost about $50 a pair. If you can move up a grade, you'll likely get better functioning whichever you buy.
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