On price, InterServer starts lower at $2.50/mo against $4.15/mo for Hetzner. Hetzner carries the higher rating overall, at 4.8/5, and Hetzner reports the better tracked uptime at 99.90%. Hetzner has been operating longer, since 1997.
If entry price is what decides it, start with InterServer. If rating and reliability matter more than the sticker price, Hetzner 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.