The two that you have shown in your post are not all that wonderful. The Piranha operates using a very basic tech and the other is a relatively unknown brand, which may cause big issues with spares and so on. Good brands to go with when shopping for a new gun would be - Proto, Dye, Invert and Planet Eclipse
Unless you want to dress up as Rambo and cart a load of useless "upgragdes" around with you, you want to get an Electropneumatic gun. This basically means that, unlike other guns that use springs and similar to work (blowbacks), they use a solenoid to cycle air to different parts of the guns to make it fire. They will be smoother, lighter and just generally lovelier than BBs. Buy a gun that is suitable for tournament play, which will then be suitbale for woodsball as well: woodsball guns tend to look like real military hardware, but are too bulky heavy and slow firing to be any use when playing games on smaller fields or tournament fields.
Personally, I would buy the gun secondhand. The secondhand market is in freefall and you can buy kit for ridiculous money secondhand! Make sure you stick to well known brands and sellers on here with good feedback and you'll do fine. Guns that are avaialble for <£150 include:
Proto PMR -90ish
Proto SLG - 60ish
Ion - 70ish
Ego 05 - 150ish
Etek Ego 1 - 150ish
All are excellent markers, and silly value at that money. chuck in a Halo or Reloader Hopper (£35ish) a steel air tank (£35ish) and spend as much as you can on a brand new mask and you have an excelent set up that will keep up with pretty much anything out there...