TescoMobile have some very good plans, a reasonable range of phones and their plans allow tethering. My plan (SIM only) is unlimited texts, unlimited calls to Irish mobiles / landlines (excludes non-geographic / premium numbers 1890 / 1850, etc). 15 gb / month data, foreign calls @ 1c / minute, all for €35/month inc VAT and ClubCard points on the DD payments.
Plans & offers change often so check all the websites.
With regard to handsets, I have always bought Nokia (or Motorola when they were around). The battery in my E63 was giving problems so I dug my 12-year old 6310i out of a drawer while waiting for a replacement. I put the TescoMobile SIM in and the phone powered up immediately. I unlocked it for the new network and its running like a watch since.