These days, solid hardwood flooring comes in a wide variety of different formats, from plank, blocks and battens, through to strip and mosaics. Furthermore, each of these formats also come either pre-finished or unfinished and in almost any wood species you can imagine.
The main advantage of solid wood flooring over engineered flooring is its ability to be resanded and refinished over many years. As such, it is not uncommon for solid wood floors to last 50 years or more.
The main issue to consider with solid wood floors is because they are solid wood, they are less dimensionally stable than engineered wood floors, and are more susceptible to expansion and contraction due to temperature and humidity changes in the home. As a broad rule of thumb; the wider and thicker that a board is, the more it has the capacity to expand or contract. Some of the very wide oak planks that are available these days at around 220mm wide, require top-fixing for this reason.
Solid wood flooring is generally not suitable for underfloor heating; the most appropriate wood floor for fitting over underfloor heaing is engineered, ideally Multi-layer engineered flooring. In either instance, to accommodate this movement, all wood floors are installed with a 10mm to 15mm gap around the perimeter of the floor along the wall and the gap is covered up by the skirting board or alternatively a scotia or quadrant beading. The only exception to this might be where a wood block, mosiac or traditional parquet is fitted, where the scope for expansion is sometimes allowed for in a flush, inset cork border.