On price, InterServer starts lower at $2.50/mo against $35/mo for Kinsta. Kinsta carries the higher rating overall, at 4.9/5, and Kinsta reports the better tracked uptime at 99.99%. InterServer has been operating longer, since 1999.
If entry price is what decides it, start with InterServer. If rating and reliability matter more than the sticker price, Kinsta has the edge. Either way, read the full profile before you buy — the trade-offs section on each page covers what the summary numbers leave out.